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SHORE PROCESSES 

AND 

SHORELINE DEVELOPMENT 



BY 



DOUGLAS WILSON JOHNSON 

Associate Professor of Physiography, 
Columbia University 



FIRST EDITION 



NEW YOKK 

JOHN WILEY & SONS, Inc. 

London: CHAPMAN & HALL, Limited 

1919 



($K 



& 



r& 



Copyright, 1919, by 
DOUGLAS W. JOHNSON 



Copyrighted in Great Britain 



MAY \2 1919 



Stanbope {press 

F. H.GILSON COMPANY 
BOSTON, U.S.A. 






A525451 



' / 



^o 



PREFACE 

The present work was born of a need experienced by the author 
in connection with his shoreline studies. In the course of a critical 
examination of the arguments supposed by many to demonstrate 
a progressive subsidence of the Atlantic coast of North America 
within historic time, it developed that in respect to certain of these 
arguments agreement between students of the problem could not 
be reached because there was not sufficient agreement as to what 
features are normally characteristic of a stable coast ; and what 
features are peculiar to coasts which are rising or subsiding. No 
work existed which combined with an extended analysis of the 
forces operating along the shore, a full and systematic discussion 
of the cycle of shoreline development and such further discussion 
of the modifying effects of changes of level as would enable one to 
differentiate stable, rising, and subsiding coasts. 

It seemed necessary, therefore, to enquire somewhat fully into 
the fundamental principles of shore processes and shoreline de- 
velopment; for it would not be profitable to add to the already 
overburdened literature on changes of level another essay which 
should merely add quantitatively to the volume of evidence pre- 
viously discussed by many earlier writers, and again assert as the 
correct interpretation of that evidence conclusions which some 
geologists and geographers accept and others reject. Profit could 
come from the study only in case the discussion of principles was 
such as to bring geologists and geographers into substantial agree- 
ment as to what shore features are, and what are not indicative of 
changes of level. Once this measure of agreement was reached, I 
could not doubt that a critical analysis of the arguments supposed 
to prove the progressive subsidence within historic time of the 
coast of southeastern Canada, the Atlantic coast of the United 
States, and certain other marginal areas of the continents, would 
demonstrate to the impartial and. critical student the inadequacy 
of those arguments. I therefore set myself the task of bringing 
together the results of shoreline studies published in different 
languages, of analyzing and criticising the conclusions reached 



iv PREFACE 

where this might appear to be profitable, and of presenting a digest 
of those fundamental principles which should prove to be best 
established by the independent work of different students and 
best supported by my own field observations. At the seme time 
I purposed to develop somewhat fully certain important aspects of 
the physiography of shorelines which have hitherto received little 
consideration. 

The magnitude of the task proved to be greater than antici- 
pated, partly because of the wide divergence of expert opinion 
regarding the manner in which shore processes operate, and partly 
because of the great volume and scattered distribution of the 
writings dealing with the subject. It was, indeed, the desire to 
relieve others who might have occasion to study shore processes 
and shoreline forms, of the burden of duplicating the work involved 
in my undertaking which first suggested to me the desirability of 
placing on record, in compact form for their use, the results of my 
enquiry, even where these results did not relate to the original 
problem of coastal subsidence. The present volume is the con- 
crete product of this desire to render a service to my fellow 
students. 

The engineer will find in the chapters on waves and currents a 
summary of the widely conflicting opinions and observations re- 
lating to those most puzzling forces with which he has to deal. 
In the later chapters he will also find, I hope, not a few discussions 
of shore forms and of the method of their development which will 
prove useful to him in his work on marine engineering structures. 
The dynamic geologist will find in the first chapters an extended 
account of two of the forces of nature with which he is much con- 
cerned, and in the remaining chapters abundant illustrations of 
the manner in which those forces operate near the margins of the 
lands. The geographer will be mainly concerned with the last 
seven chapters where the forms of the shoreline receive a syste- 
matic treatment which, if not adequate, is at least somewhat more 
detailed and complete than any hitherto attempted. Throughout 
the volume the reader will note that repeatedly conclusions 
reached and principles established are briefly applied to the prob- 
lem of changes of level; and he will understand that this is the 
thread, appearing now and then, which is to connect parts of the 
present study with a later volume devoted exclusively to the much 
mooted question of coastal subsidence. 



PREFACE V 

As a rule an advance summary precedes, and a brief resume con- 
cludes the text of each chapter. This will enable engineer, geolo- 
gist and geographer to determine in some measure the extent to 
which matters pertinent to their respective fields are discussed. 
A bibliography, arranged alphabetically according to authors and 
placed at the end of the volume, supplements the list of references 
given at the close of each chapter. Finally, an index of authors 
and an index of subjects are provided in the form which it is hoped 
will prove most serviceable to the reader. 

In any attempt to give proper credit for the aid rendered by 
others during the preparation of this volume the writer is much 
embarrassed. The work of preparation has extended over several 
years, during which time a number of students, colleagues and 
friends have been most generous in rendering valuable assistance. 
It would be impossible to make specific acknowledgments to all of 
them, so great is the measure of my indebtedness. Special thanks 
are due to my cousin, Miss Laura Dale Johnson, for assuming 
the labor of reading the proofs and seeing the book through the 
press during my absence; to Miss Florrie Holzwasser of the De- 
partment of Geology of Barnard College, and others among my 
graduate students, for assistance in reviewing and abstracting the 
literature relating to the subject in hand; and to Dr. A. K. Lobeck 
for preparing the five block diagrams showing successive stages 
in the development of a shoreline of submergence. Acknowledg- 
ments should be made to "The Geographical Review," "Science," 
the "Bulletin of the Geological Society of America," and the 
"Journal of Geology" for the use of certain material originally 
published in their pages. Many of the observations recorded in 
this volume were made in the course of a special Shaler Memorial 
Investigation of the problem of coastal subsidence undertaken 
with the support of the Shaler Memorial Fund of Harvard Uni- 
versity; and observations on the New Jersey coast were obtained 
in connection with a study in progress for the Geological Survey 
of New Jersey under the direction of Dr. H. B. Kummel. It is a 
pleasure to express special obligations to Professor W. M. Davis 
for helpful criticism of the manuscript, and to acknowledge the 
debt which all physiographers owe to his studies of shoreline 
topography, which were the first to demonstrate the value of 
applying the idea of the cycle to the history of shore forms. To 
Professor Joseph Barrell, whose studies have to some extent paral- 



vi PREFACE 

leled certain of my own, I am indebted for many valuable sugges- 
tions and for his generous courtesy in giving to the manuscript a 
careful and critical reading, from the results of which I have greatly 
profited. 

In conclusion it is but fair to acknowledge the author's keen 
appreciation of certain defects which the reader may discover in 
his perusal of the text. The volume goes to press under circum- 
stances which absolutely prevent that careful attention to details 
which every work of this kind should receive. On entering the 
service of his country the writer was forced to choose between 
publishing his studies without the final supervision which he had 
hoped to give the proofs, and postponing publication indefinitely. 
In view of the uncertainties attending service in the zones of mili- 
tary operations, it has seemed wiser to allow the work to go to 
press, in the hope that the indulgent reader will not find the value 
of the volume materially affected by such errors in execution as 
the presence of the author alone could have prevented. 

DOUGLAS WILSON JOHNSON. 
On Board Troop Ship, 
April 3, 1918. 



CONTENTS 

Page 

List of Plates ix 

List of Illustrations xiii 



CHAPTER I 

Water Waves 1 

Advance summary, 1; Scope of subject, 2; Literature, 4; Waves 
of oscillation, 7; Origin, 7; Wave motion, 8; Wave form, 12; Wave 
height, 21; Wave length, 27; Wave velocity, 29; Waves of transla- 
tion, 33; Earthquake and explosion waves, 38; Tidal waves, 41; 
Standing waves; seiches, 42; Boundary waves, 44; Resume, 45; 
References, 46. 

CHAPTER II 

The Work of Waves 55 

Advance summary, 55; Wave energy, 55; Nature of wave attack, 
57; Wave dynamometer, 62; Measurements of wave energy, 63; 
Damage by storm waves, 65; Conditions affecting wave energy, 
72; Wave refraction, 74; Depth of wave action, 76; Resume, 83; 
References, 83. 

CHAPTER III 

Current Action 87 

Advance summary, 87; Types of currents, 88; Wave currents, 90; 
Tidal currents, 106; Seiche currents, 122; Wind currents, 123; 
Planetary currents, 128; Pressure currents, 130; Convection cur- 
rents, 131; Salinity currents, 131; River currents, 136; Reaction 
currents, 138; Eddy currents, 139; Deflection of currents, 141; 
Resume, 148; References, 149. 

CHAPTER IV 

Terminology and Classification of Shores 159 

Advance summary, 159; Terminology of shores, 159; Plains, 
planes, and peneplanes, 164; Classification of shorelines, 169; I. 
Shorelines of submergence, 173; II. Shorelines of emergence, 186; 
III. Neutral shorelines, 187; IV. Compound shorelines, 190; 
Stages of shoreline development, 192; Resume, 192; References, 
192. 



Vlll CONTENTS 

CHAPTER V 

Page 

Development of the Shore Profile 199 

Shorelines of submergence, 199; Advance summary, 199; Initial 
stage, 201; Young stage, 203; Mature stage, 210; Old stage, 224; 
Validity of the theory of a marine cycle, 228; Correlation of the 
marine and fluvial cycles, 242; Independence of marine and fluvial 
cycles, 245; Comparative rapidity of marine and fluvial planation, 
249; Probability of marine planation, 253; Interruptions and acci- 
dents during the marine cycle, 257; Shorelines of emergence, 258; 
Initial stage, 258; Young stage, 259; Mature and old stages, 262; 
Neutral shorelines, 262; Compound shorelines, 265; Resume, 267; 
References, 268. 

CHAPTER VI 

Development of the Shoreline 272 

A. Shorelines of submergence, 272; Advance summary, 272; 
Initial stage, 272; Young stage, 275; Stages of development of 
shore details, 328; Relative importance of different marine forces in 
the formation of bars, forelands, etc., 333; Mature stage, 339; 
Old stage, 344; Resume, 345; References, 345. 

CHAPTER VII 

Development of the Shoreline (Continued) 348 

B. Shorelines of emergence, 348; Advance summary, 348; Initial 
stage, 348; Young stage, 350; Effect of progressive subsidence on 
lagoon history, 383; Effect of progressive elevation on lagcon his- 
tory, 386; Offshore bars not an evidence of subsidence, 386; Mature 
stage, 389; Old stage, 390; Resume, 392; References, 392. 

CHAPTER VIII 

Development of the Shoreline (Continued) 395 

C. Neutral and compound shorelines, 395; Neutral shorelines, 
395; Compound shorelines, 400; Contraposed shorelines, 401; 
References, 403. 

CHAPTER IX 

Shore Ridges and Their Significance 404 

Advance summary, 404; Origin of beach ridges, 404; Rate of 
beach ridge formation, 414; Beach ridges as records of changes of 
level, 439; Resume, 453; References, 454. 

CHAPTER X 

Minor Shore Forms 458 

Advance summary, 458; Beach cusps, 458; Low and ball, 486; 
Ripple marks, 489; Rill marks, 512; Swash marks, 513; Backwash 
marks, 517; Sand domes, 518; Shore dunes, 519; Resume, 525; 
References, 525. 



LIST OF PLATES 

Page 
I. Storm waves breaking against seawall at Hastings, England . 1 4 
II. Combing wave, showing water completing orbital move- 
ment although insufficient in quantity to fill the wave 
form 17 

III. Waves breaking against seawall at Scarborough, England. . 19 

IV. Storm wave striking face of seawall at Scarborough, England 59 
V. Water forced vertically upward by wave breaking against 

seawall at Scarborough, England 61 

VI. Marine Cliff at Highland Light, Cape Cod, rapidly retreat- 
ing under wave attack 64 

VII. Shakespeare's Cliff near Dover, England 79 

VIII. Wire fence undermined by wave attack and left hanging in 

mid-air 73 

IX. Cobblestones cast into a high ridge well above sealevel by • 

storm waves 78 

X. Cobblestones cast upon the beach from deep water through 
the combined effect of wave action and the buoyancy of 

attached seaweeds 92 

XI. Surf breaking on the shore of Cape Canaveral, Florida .... 95 
XII. Winthrop Great Head, a wave-cliffed drumlin near Boston, 

Massachusetts 98 

XIII. Lowestoft Ness on the east coast of England 102 

XIV. Giant sand ripples produced by strong ebb tide current in 

the Avon River estuary near Windsor, Nova Scotia 110 

XV. Salt marsh near Green Harbor, Massachusetts 112 

XVI. Hornviken, a small fjord near North Cape, Norway, showing 

typical oversteepened walls of a glacial trough 175 

XVII. Idde Fjord near Fredriksten, Norway, showing rectangular 

pattern characteristic of many fjord coasts 178 

XVIII. The Naero Fjord, Norway, a partially submerged glacial 

trough 180 

XIX. Lake Loen, Norway, occupying a glacial trough and practi- 
cally continuous with the upper part of Nord Fjord .... 183 
XX. Stromstad Harbor, Sweden, showing characteristics of a 

fiard coast 185 

XXI. Northwestern coast of France near Fecamp, showing youth- 
ful cliff profiles on a mature shoreline of submergence . . . 200 
XXII. Same view as Plate XXI, but at low tide, showing marine 

cliff, wave-cut bench, and narrow beach at base of cliff . . 202 
XXIII. Marine cliff cut in glacial drift near Plymouth on the Mas- 
sachusetts coast 205 

ix 



X LIST OF PLATES 

Page 
XXIV. Marine cliff cut in sand and clays of the coastal plain near 

Beaufort, North Carolina 207 

XXV. Marine cliff cut in sand dunes on the shore of Cape Cana- 
veral, Florida 1209 

XXVI. View near Rhuvaal, Islay, off the west coast of Scotland, 
showing former marine cliff and wave-cut bench, recently 

elevated above sealevel 227 

XXVII. Elevated marine cliff near Oban, Scotland 233 

XXVIII. Marine cliff and wave-cut rock bench on the Pacific coast 

south of Cape Flattery, Washington 236 

XXIX. Marine peneplane and monadnock near Madura, east coast 

of India 239 

XXX. Base of monadnock in Plate XXIX, showing effects of 

marine erosion 241 

XXXI. Monadnock on marine peneplane of the east coast of India . 251 
XXXII. Imposing marine cliff at North Cape, Norway 252 

XXXIII. Rocky headland and drowned valley of a young shoreline of 

submergence, near Clifton, Massachusetts 255 

XXXIV. Stack or chimney in front of a young cliff on the coast of 

France 277 

XXXV. The Dogstone, near Oban, Scotland, a stack in front of a 

marine cliff, now elevated 25 feet above sealevel 279 

XXXVI. Fingal's Cave on the Island of Staffa, western Scotland. . . . 280 
XXXVII. Ancient sea cave on an elevated shoreline of western Scot- 
land, transformed into a stable 282 

XXXVIII. Wave-cut arch on the northwest coast of France 284 

XXXIX. Third Cliff near Scituate, Massachusetts, showing small 

landslide due to wave erosion of cliff base 286 

XL. Bay-head or pocket beach near Rye, New Hampshire 288 

XLI. Deltas of cobblestone formed by overwash of storm waves 

near Marblehead, Massachusetts 305 

XLII. Tombolo connecting the former island of Marblehead with 

the Massachusetts mainland 314 

XLII I. Hanging valleys on the chalk coast of southeastern England, 
where waves cut back the shore faster than the streams 

can deepen their valleys 342 

XLIV. Former offshore bar near Wrightsville, North Carolina, 
rising above the marsh surface back of the present off- 
shore bar 353 

XLV. Surface of a salt marsh near Boston, Massachusetts, which 
overlies a peat deposit 20 feet deep composed of remains 

of high-tide vegetation 384 

XLVI. Contraposed shoreline south of Rye Beach, New Hampshire. 402 
XLVII. Ancient beach ridge (center of view) connecting former 

island in distance with one in foreground 406 

XLVIII. Ancient series of dune ridges on Cape Canaveral, truncated 
at right angles by a later series in the foreground, on one 
member of which the man is sitting 415 



LIST OF PLATES xi 

Page 
XLIX. Shingle beach ridges of the Dungeness cuspate foreland, 

England 421 

L. Shingle beach ridges on the island of Riigen, Germany .... 425 
LI. Forested dune ridges on the Darss cuspate foreland, Ger- 
many, showing marked inequality in altitude of crestlines 427 
LII. Road-cut through an old dune ridge at the back of the 

present shore at Daytona, Florida 432 

LIII. Successive curving beach ridges and swales forming lines of 

growth on Cape Canaveral 441 

LIV. Level surface of Skanor peninsula, southwestern Sweden. 448 
LV. Beach cusps of gravel on the shore of Carmel Bay, California 452 
LVI. Giant sand cusps on Melbourne Beach, Florida, truncated 

J by wave erosion 464 

LVII. Cusps on Nantasket Beach, Massachusetts 468 

LVIII. Beach cusps on the west coast of Porto Rico, near Melones 

Point 472 

LIX. Sandstone slab showing fossil oscillation ripples 490 

LX. Current ripples formed by an ebbing tide 492 

LXL Current ripples on the shore of Nantasket Beach, Massa- 
chusetts 493 

LXII. Giant current ripples near Annisquam, Massachusetts, 
showing irregular pattern due to interference of wave and 

tidal currents 499 

LXIII. Current ripples near Windsor, Nova Scotia 503 

LXIV. Current ripples modified by later oblique wave or current 

action 506 

LXV. Plaster cast of interference ripple mark formed by two 

systems of waves crossing nearly at right angles 507 

LXVI. Rill marks on a sandy beach 511 

LXVII. Plaster cast of swash marks left by four successive waves 

on the sandy shore of Lake Erie 514 

LXVIII. Cast of backwash marks 515 

LXIX. Plaster cast of backwash marks 516 

LXX. Shore dunes of the Holland coast near Katwijk 520 

LXXI. Shore dunes near Scheveningen, Holland 521 

LXXII. Dune of barchane form overwhelming trees on the Province- 
lands of Cape Cod 522 

LXXIII. Shore dunes near Cape Henry, Virginia, migrating iniand 

over the forest 524 



LIST OF ILLUSTRATIONS 

Frontispiece. Wave-cut bench and marine cliff bordering Desecheo 
Island, Porto Rico, recently elevated above sealevel. 
Fig. Page 

1. Diagram showing the motion of water particles in an oscillatory 

wave 9 

2. Diagram showing the elliptical orbits of water particles in shallow- 

water waves, and the decrease in size of orbits with increasing 
depths 10 

3. Diagram showing theoretical form of a cycloidal wave, and the 

rapid decrease in size of the orbits (through which the water par- 
ticles move) with increasing depth 12 

4. Theoretical profiles of three trochoidal waves having different sized 

orbits (solid-line profile and broken-line profile), or different 
spacing of orbits (broken-line profile and dotted-line profile). 13 

5. Diagram showing how two regular series of waves of different 

heights and lengths combine to form an irregular series 26 

6. Diagram showing movement of water particles in a wave of trans- 

lation 34 

7. Diagram showing how oscillatory waves breaking on a subaqueous 

terrace produce waves of translation 37 

8. Diagram to illustrate the movement of water particles in standing 

1 waves, such as the seiche . . 43 

9. Boundary wave formed by local air current over liquids of different 

densities 44 

10. Diagram showing movement of water particles in overlying fresh 

water and underlying salt water during the passage of bound- 
ary waves from left to right 44 

11. Stevenson's wave dynamometer , . . c 62 

12. Diagram to illustrate the process of wave refraction, whereby wave 

attack is concentrated on headlands , 75 

13. Section of beach slope showing by dotted lines the so-called zig-zag 

path of debris particles during beach drifting and by solid lines 

the parabolic paths actually followed 94 

14. Parabolic paths of large and small particles of debris subject to 

beach drifting , 96 

15. Parabolic paths followed by debris particles impelled by tne com- 

bined action of on-shore swells and oblique wind waves 97 

16. Diagram to illustrate relation of beach drifting to wind directions 100 

17. Parabolic paths of debris particles subject to beach drifting 101 

18. Elliptical orbit of water particle during passage of the tide wave 

over a sloping seabottom 106 

19. Course followed by a nearly submerged float under the influence 

of tidal currents in New York harbor , „ . . . . . 116 

xiii 



XIV LIST OF ILLUSTRATIONS 

Fig. Page 

20. Theoretical course calculated by Parsons for the float whose actual 

course is shown in Figure 19 118 

21. Eddy currents in the Gulf of Honduras and Mosquito Gulf 140 

22. Elements of the shore zones during an early stage of development . 160 

23. Elements of the shore zones in an advanced stage of development. 162 

24. Embayed coastal plain of Chesapeake Bay region, showing example 

of ria shoreline 174 

25. A typical section of the fjord coast of Norway, showing angular 

pattern attributed to fault-control 177 

26. Mississippi Delta 187 

27. Delta of the Tiber 188 

28. Niger Delta 189 

29. Initial stage of a fault shoreline 190 

30. Coast of North Carolina, showing one type of compound shoreline. 191 

31. Compound shoreline due to faulting and partial submergence of up- 

throw block 191 

32. Stages in the development of the shore profile of a shoreline of sub- 

mergence . 201 

33. Successive profiles of equilibrium on a retrograding shore 211 

34. Profiles of equilibrium off the Madagascar coast as plotted from 

charts by Barrell 212 

35. Stages in the development of the shore profile of a shoreline of sub- 

mergence 213 

36. Variations in the beach profile of equilibrium due to variations in 

the different shore forces 218 

37. Mature and old shore profiles of a shoreline of submergence 224 

38. San Clemente Island off the coast of southern California, showing 

series of uplifted wave-cut terraces 229 

39. Cross-section of the western coast and continental shelf of Norway. 232 

40. Stages in the reduction of a land mass 256 

41. Overlapping of marine deposits upon the abrasion platform of a 

slowly subsiding land mass 258 

42. Elements of the profile of a shoreline of emergence 258 

43. Stages in the development of the shore profile of a fault coast .... 264 

44. Profile of a shoreline of emergence 266 

45. Shoreline of submergence, initial stage 273 

46. Shoreline of submergence in Chesapeake Bay region 274 

47. Early youth of a shoreline of submergence, showing crenulate shore- 

line 275 

48. Crenulate shoreline of the southwest coast of Ireland 276 

49. Young shoreline of submergence near Idzuhara, Japan, showing 

crenulate stage 278 

50. Young shoreline of submergence, showing types of beaches, bars, 

spits, and forelands 283 

51. Initial unorganized condition of currents along a young shoreline 

ot submergence compared with organized condition which ob- 
tains when the stages of submaturity or maturity are reached . . . 285 

52. Sand spits on the shore of Port Orchard, Washington 287 



LIST OF ILLUSTRATIONS XV 

Fig. Page 

53. Simple spit and compound recurved spit at entrance to Port 

Moller, Alaska 289 

54. Successive stages in the development of one type of compound re- 

curved spit 291 

55. Compound recurved spit enclosing Toronto Harbor 293 

56. Development of the Cape Cod shoreline 294 

57. Development of Sandy Hook spit 296 

58. Lagoons and ridges of the Presque Isle compound recurved spit.. . 299 

59. Spits built by converging currents 300 

60. Spits converging to form a bay bar on the Alaskan coast 300 

61. Bay-mouth bars on the Marthas Vineyard coast 301 

62. Bay-mouth bar on the Marthas Vineyard coast 302 

63. Bay-head bar near Duluth 303 

64. Mid-bay bar in Hempstead Harbor, Long Island 304 

65. Winged headland near Sag Harbor, Long Island 306 

66. Offsets, overlaps, and stream deflection „ . 308 

67. Looped bar on shore of Shapka Island, Alaska 310 

68. Renard Island near Seward, Alaska, showing embankment growing 

from island toward mainland 311 

69. Inner Iliasik Island, Alaska, showing embankment which may be 

upbuilding toward the surface simultaneously along its entire 

length 311 

70. Single tombolo connecting former island of Marblehead with the 

mainland 312 

71. Former island of Big Nahant tied to Little Nahant, and the latter 

to the mainland by single tombolo 313 

72. Duxbury and Saquish Neck tombolos uniting former islands with 

the mainland of Massachusetts near Plymouth 316 

73. Monte Argentario, Italy, tied to the mainland by a double tombolo 317 

74. Morro del Puerto Santo, Venezuela, a Y-tombolo 318 

75. Former islands, many of which were wholly or completely eroded by 

wave action, and the resulting debris used by the waves to build 

a complex tombolo tying the remaining islands to the mainland. 319 

76. Nantasket Beach, Massachusetts, the complex tombolo formed by 

wave erosion of the islands shown in Fig. 75, with deposition of 
the debris to give connecting beaches uniting the remaining 

islands with each other and with the mainland at the south. 320 

77. A strongly recurved spit on the Washington coast, about to become i 

a cuspate bar 321 

78. Cuspate bars on the Narragansett Bay shore 321 

79. Cuspate bar, showing enclosed marsh near Providence, Rhode 

Island 321 

80. Cuspate bar originally built as a tombolo tying to the mainland an 

island since removed by wave erosion 321 

81. Cuspate bars on the shores of Port Discovery, Washington 323 

82. Cuspate foreland near Port Townsend, Washington 324 

83. Types of cuspate foreland bars 324 

84. The former Cape Canaveral, now known as False Cape 326 



xvi LIST OF ILLUSTRATIONS 

Fig. Page 

85. Marsh bars on the Delaware Bay shore 327 

Comparison of text figures to facilitate correlations of successive 

stages in the development of a shoreline of submergence 331 

86. Lake Balaton (Platten Lake), showing position of cuspate bar . . . 337 

87. Shoreline of submergence, submature stage 340 

88. Shoreline of submergence, mature stage 341 

89. Valleuses on the northwest coast of France 343 

90. Theoretical profile through offshore bar 357 

91. Theoretical profile through offshore bar 357 

92. Theoretical profile through offshore bar 357 

93. Theoretical profile through offshore bar 358 

94. Theoretical profile through offshore bar 358 

95. Theoretical profile through offshore bar 359 

96. Theoretical profile through offshore bar 359 

97. Profile through offshore bar 361 

98. Profile through offshore bar 361 

99. Profile through offshore bar 361 

100. Profile through offshore bar 361 

101. Profile through offshore bar 361 

102. Profile through offshore bar 363 

103. Profile through offshore bar 363 

104. Profile through offshore bar 363 

105. Profile through offshore bar 363 

106. Profile through offshore bar 363 

107. Profile through offshore bar 363 

108. Profile through offshore bar 364 

109. Profile through offshore bar 364 

110. Profile through offshore bar 364 

111. Profile through offshore bar 364 

112. Profile through offshore bar 364 

113. Profile through offshore bar 364 

114. Profile through offshore bar 364 

115. Offshore bar and lagoon of the Long Island coast, showing distribu- 

tion of tidal inlets 371 

16. Offshore bar and lagoon of the New Jersey coast 371 

17. Tidal delta at Ocracoke Inlet, North Carolina coast 375 

18. Stages in the development and retrogression of an offshore bar. 376 

119. Stages in the normal history of an offshore bar, due account being 

taken of the effect of migrating inlets 378 

120 . Diagram showing how wave erosion of a lobate delta may transform 

it into an arcuate delta (broken line) 396 

121. Fault shoreline bordering a scarp which dies out toward the right 397 

122. Similar to Fig. 121, except that the fault traversed a little dissected 

plain of faint relief 398 

123. Successive stages in the retrogression of a fault shoreline bordering 

rocks of varying resistance 399 

124. Compound shoreline, combining essential features of a shoreline of 

submergence and a fault shoreline 40] 



LIST OF ILLUSTRATIONS XV11 

Fig. Page 

125. Stages in the formation of a contraposed shoreline 403 

126. Cuspate delta of the Tagliamento River, Italy, showing parallel 

beach ridges 410 

127. Successive stages in the development of Ro'ckaway sand spit, Long 

Island 417 

128. Diagram of cliffed headland and associated beach ridge plain, show- 

ing that one series of ridges truncating another does not neces- 
sarily imply a longer lapse of time than an equal number of 

parallel ridges 418 

129. Ridges of the Cape Canaveral cuspate foreland 420 

130. The Dungeness cuspate foreland, showing shingle beach ridges and 

swales 423 

131. Dune ridges of the Darss cuspate foreland, Germany 429 

132. Dune ridges of the Swinemunde tombolo 434 

133. Beach ridges indicating coastal emergence 446 

134. Beach ridges indicating coastal submergence . 447 

135. Hypothetical case in which beach ridges on a rising coast may give 

a false indication of stability 449 

136. Hypothetical case in which beach ridges on a sinking coast give a 

false indication of stability 450 

137. Types of beach ridges formed on a stable coast 451 

138. Beach ridges of equal height 'separated by swales of different depths 

due to variations in spacing of ridges 453 

139. Diagram illustrating Branner's theory of beach cusp formation . . . 461 

140. Diagram illustrating Branner's theory of the formation of unequally 

spaced beach cusps 461 

141. Variations in the form of beach cusps 465 

142. Partially eroded older cusps and respaced later series 466 

143. Normal and inverted beach cusps 473 

144. Artificial beach cusps 476 

145. Beach cusps (after Jefferson) showing compound cusps at right. . . 484 

146. Oscillation ripples -. 491 

147. Current ripples 494 

148. Vortices involved in the formation of current ripple mark 497 

L49. Sand dome 518 



SHOKE PEOCESSES AND 
SHOEELINE DEVELOPMENT 



CHAPTER I 
WATER WAVES 

Advance Summary. — No adequate appreciation of the many 
problems presented by the shoreline can be gained until one 
is familiar with the work of waves and currents. The relative 
importance of these two forces in shaping the shore is a much 
disputed point; and the difficulties involved can best be set 
forth, and an attempt at their solution can best be made, if we 
review the essential characters of waves and currents with some 
care, and critically examine the manner in which each operates. 
We will first turn our attention to the phenomena of water waves 
of different types; then we will be in a position to discuss the 
work accomplished by such waves; after which currents and 
their work will be considered. 

In this first chapter, after a note on the general scope of the 
present treatment of waves, there is presented to the reader a 
brief survey of the literature on the subject, which may be 
useful in showing the growth of our knowledge of waves since 
the time of Leonardo da Vinci. Attention is then directed to 
the two types of waves which are most effective in shore proc- 
esses: the wave of oscillation and the wave of translation. In 
each case the origin and nature of the water movement are ex- 
plained and the elements of wave form are described. The 
depths at which waves break on approaching a coast determine 
the position of certain shore forms, and therefore receive con- 
sideration. The factors affecting the height of waves are of 
vital interest to the engineer employed on harbor works or 
coast defenses, and to the student of shore forms produced 
under varied conditions of wave attack; hence these factors 

1 



2 WATER WAVES 

are discussed with some fullness. A wave's capacity for de- 
struction depends upon both its height and its length, and the 
velocities of certain waves vary with wave length according to 
definite laws. The lengths of waves and their velocities are 
therefore matters of importance to engineer and geologist, and 
the natural laws which govern them possess a fascinating in- 
terest for the laymen interested in one of the most impressive 
of Nature's destructive forces. 

Earthquakes and explosion waves are comparatively rare phe- 
nomena, but their spectacular character, the popular interest 
w T hich attaches to them, and the disasters for which they are 
responsible, entitle them to consideration in any treatise on 
waves. The great wave known as the "tide " is of importance 
to the student of shore processes only in connection with the 
currents which it produces, and is accordingly given scant space 
in Chapter I. A treatment of tidal currents will be found in 
Chapter III. Standing waves including the seiche, and the 
so-called " boundary waves " produced at the contact of liquids 
having different densities, are of theoretical rather than prac- 
tical interest in the present connection, and are discussed very 
briefly. 

Scope of Subject. — Water waves may be produced in a variety 
of ways. The bow of a vessel pushing through the water, or a 
strong wind blowing over the sea, or a rain-drop falling into it, will 
each produce waves; but in each case the waves are of essentially 
different character, and behave according to distinctly different 
laws. One of the waves generated by a submarine displacement of 
the earth's crust is similar to the wave pushed out from the bow of 
a moving ship, but is unlike those produced during a storm at sea. 
Waves which form when a fine wire is drawn through the water 
behave very differently from the ship's waves, but are like the 
ripples set in motion by a falling drop of water. The great wave 
known as the " tide " is a compound wave, combining some of 
the characteristics of the two groups of waves first mentioned. 
When wind-made waves break on a shallow shore they give 
rise to a new series of waves similar to those produced by the 
bow of a vessel. Such facts as these are sufficient to show that 
the subject of waves is an extremely complicated one. Op- 
portunity for making direct observations of wave motion below 
the surface of water bodies in nature is very limited, while the 



SCOPE OF SUBJECT 3 

theoretical treatment of wave motion carries one into the realms 
of higher mathematics. 

It is not within the scope of the present report to enter into a 
discussion of all the interesting series of water waves known to 
science. The beautiful and complicated wave pattern developed 
by a moving ship has little to do with the modelling of shore 
forms, and the reader who would follow that phase of the sub- 
ject further is referred to Lord Kelvin's popular lecture " On 
Ship Waves" 1 , the second chapter of J. A. Fleming's little volume 
on " Waves and Ripples " 2 , and the twelfth chapter of Vaughan 
Cornish's book entitled " Waves of the Sea and other Water 
Waves " 3 , in which latter place will be found exquisite photo- 
graphic illustrations of ship waves. The phenomena of ripples 
are treated at some length by Fleming 4 , and a more technical 
account is given by J. Scott Russell 5 . Other interesting forms 
of water waves are described at length by Russell 6 and Vaughan 
Cornish 7 . We must confine our discussion to those types of 
wave motion which have a significant effect upon the shore. 

But even if we limit ourselves to a consideration of those waves 
of practical importance to the engineer and physiographer, our 
task is by no means an easy one. The literature of the subject is 
extensive and much of it highly technical in character. Different 
authorities employ different formulae in deriving some of the 
elements of wave motion, and the results they obtain agree 
neither with each other nor with the results obtained by experi- 
mentation. Airy commends the experimental work of J. Scott 
Russell as being the best ever done, but warns the reader against 
accepting that author's theoretical expressions, claiming that 
his own formulae express the true relations and are verified by 
Russell's results 8 . Russell, in turn, demonstrates the inaccu- 
racy of Airy's formulae, and deplores the fact that the methods 
of investigation employed by that able authority should not have 
led him to better conclusions 9 . Hagen likewise opposes with 
some vigor certain of the suppositions made by Airy, while the 
experimental observations of Caligny and Russell disagree on 
important points. Krummel has well expressed the present con- 
dition of the subject in the words: " In short analysis, observa- 
tion and experiment are not yet in the desired agreement " 10 . 
Fortunately, a number of the disputed points are not of special 
importance to the student of shore forms, however much he 



4 WATER WAVES 

may be interested in the complex but beautiful laws which govern 
the motions of waves. 

Literature. — Some of the principal sources of information 
upon which I have relied, and^to which the student of waves is 
referred for elaborate discussions, may briefly be mentioned. 
Of historical interest are the work of Leonardo da Vinci, who in 
the latter part of the fifteenth century recognized many of the 
fundamental principles of wave motion, and advanced theories 
which are similar to those of modern investigators; and of 
Newton, who a century later gave us the first exact mathematical 
treatment of waves. Among more recent works the publications 
of Franz Gerstner, which appeared in the early years of the nine- 
teenth century, are especially important. I have not seen the 
original papers of these authors, but their work is reviewed by 
the Weber brothers, Oialdi, Wheeler and others, in reports 
mentioned below. 

In 1809 Bremontier's able essay entitled " Recherches sur le 
Mouvement des Ondes " n was published. This early report of 
experimental work on the laws of wave action and of observations 
on wave action in nature, contains the first effective demon- 
stration of the power of waves to affect the bottom at considerable 
depths. The important volume of the two Weber brothers on 
" Wellenlehre auf Experimente gegrundet ' 12 , based on elaborate 
experimental studies and published in 1825, contains a review of 
practically everything written on waves from the time of Newton 
up to 1820, and adds much to the sum of previous knowledge 
on the subject. Six years later Emy's treatise " Du Mouvement 
des Ondes et des Travaux Hydrauliques Maritimes " 13 refuted 
Bremontier's conclusion that during wave movement the water 
particles rose and fell in vertical paths, substituted the more 
nearly correct opinion that the particles moved in vertical 
ellipses, and developed at great length the theory that a special 
type of " bottom wave " (not de fond) was the principal cause 
of changes in the forms of the coast and of the destruction of 
maritime engineering structures. Emy does not appear to have 
been familiar with the work of the Weber brothers. J. Scott 
Russell's two reports on " Waves " 14 , made to the British Asso- 
ciation in 1837 and 1842-1843, present the results of admirable 
experimental work made under conditions more favorable than 
those attending the experiments of the Weber brothers, although 



LITERATURE 5 

Russell directed his attention principally to the waves of trans- 
lation. In reading Russell's reports the student must guard 
against misapprehension arising from the fact that the text 
references to plate numbers and to the lettering of illustrations 
are full of errors. The same author's great monograph on 
" Naval Architecture " 15 contains several valuable chapters on 
waves. In 1865 there were published the results of experiments 
made during the preceding decade by Bazin and Darcy 16 on a 
much more extensive scale than those performed by Russell. 

Airy's elaborate treatise " On Tides and Waves " 17 appeared 
in the Encyclopedia Metropolitana in 1845, and has since been 
recognized as the standard mathematical discussion of the theory 
of waves, although the validity of some of his assumptions has 
been assailed. In spite of its technical character the non- 
mathematical student will find in it much of value. Two papers 
by Stokes 18 which appeared a few years later and which have 
since been included in the first volume of his " Mathematical 
and Physical Papers," are important because of their con- 
tributions to the theory of oscillating waves. Rankine gave a 
mathematical analysis of the " Exact Form of Waves near the 
Surface of Deep Water " 19 in 1863. Fourteen years later Bous- 
sinesq produced his exhaustive treatise entitled " Essai sur la 
Theorie des Eaux Courantes " 20 which includes an extended 
mathematical discussion of waves. Bertin's long " Etude sur 
la Houle et le Roulis " 21 and still more elaborate " Donnees 
Theoriques et Experimentales sur les Vagues et le Roulis" 22 
appeared in sections during the decade 1869-1879 in the Memoires 
de la Societe Nationale des Sciences Naturelles de Cherbourg, a 
publication which in the same period carried articles on the same 
or related subjects by de Saint- Venant 23 , Mottez 24 and others. 
All of these papers except the last mentioned are mathematical 
in character, but contain matter of importance for the non- 
mathematical student of wave action, the later sections of 
Bertin's second memoir including the results of experiments 
made by himself and Caligny upon the effects of waves breaking 
on sloping beaches, either with or without the disturbing effects 
of seawalls. 

In 1866 Cialdi published his important book " Sul Moto 
Ondoso del Mare e su le Correnti di esso" 25 , in which he reviews 
the works of many previous writers, particularly those of Italian 



6 WATER WAVES 

authors, and discusses wave action from the standpoint of the 
engineer. Caligny's important work on " Oscillations de PEau," 26 
published in 1883, includes the results of valuable experimental 
work on waves, particular interest attaching to his contributions 
to our knowledge of waves of translation. Stevenson's treatise on 
" The Design and Construction of Harbours " 27 contains a large 
number of facts which have materially increased our familiarity 
with the mechanical work of waves, and from the engineering 
point of view is one of the best published treatises on wave action. 
A little book on " Waves and Ripples in Water, Air and Aether " 28 
by Fleming, although representing a course of lectures given 
before a juvenile audience, presents in simple form many laws 
of wave motion which will interest the older reader. Wheeler's 
" Practical Manual of Tides and Waves " 29 reviews a few of the 
important works on waves, and discusses the principles of wave 
action at some length. A large number of interesting facts 
concerning the behavior of waves will also be found in the same 
author's volume on " The Sea Coast " 30 . Vaughan Cornish's 
beautifully illustrated book entitled " Waves of the Sea and 
other Water Waves " 31 does not consider the principles of wave 
motion very fully, but presents a wealth of facts concerning the 
height, length, and other elements of waves, and discusses the 
action of waves on shore detritus. 

The best general review of the principles of wave action which 
has come to my notice is to be found in the second volume of 
Krummel's " Handbuch der Ozeanographie " 32 . Gaillard's trea- 
tise on " Wave Action in Relation to Engineering Structures " 33 
contains a fairly extended review of the most important work 
of previous writers and discusses the results of the author's own 
excellent researches. The book loses part of its value as a ref- 
erence work because many of the quotations from the works of 
previous writers are unaccompanied by such citations of the 
original sources as would enable the reader to find them. White's 
" Manual of Naval Architecture " 34 has a valuable chapter on 
deep sea waves. The numerous papers by Vaughan Cornish, 
published in the London Geographical Journal and elsewhere, 
contain many interesting facts not stated in his book above 
mentioned; and the volumes of the " Proceedings of the In- 
stitution of Civil Engineers" (London) include a number of 
extended articles on the action of waves and currents upon 



ORIGIN 7 

shore debris, which together with the voluminous discussions 
appended, present various facts and theories of interest to the 
student of wave action. Many other' sources on which I have 
drawn are mentioned in the pages which follow. 

WAVES OF OSCILLATION 

Origin. — The waves produced by the action of the wind are 
the most important type of sea waves. When wind acts upon a 
water surface it subjects it to irregular, unequal pressure because 
winds never blow with constant velocity, but always in irregular 
gusts. Unequal pressures deform the water surface, giving it 
an undulatory form. The wind can then act directly upon the 
undulations, pressing strongly against the sides of the elevations, 
but acting less effectively against the partially protected de- 
pressions. The water in the elevations is moved forward, both 
by direct pressure and by friction with the passing air. This 
action causes the undulations to advance and to increase in size 
until the limit of wave height for the given wind velocity is 
reached, providing the breadth and depth of the water body are 
sufficiently great. 

If one watches the surface of a pond when a faint breeze 
first springs up, he will note that the once glassy surface suddenly 
becomes covered with tiny ripples, which disappear almost as 
suddenly if the breeze dies down. But if the breeze continues, 
it will be seen that these miniature waves increase in size pro- 
gressively toward the leeward side of the pond, those on the 
windward side remaining the original size. If the breeze now 
ceases suddenly, the tiny ripples on the windward side quickly 
vanish, but the larger waves developed where the wind blew 
across a greater expanse of water continue to agitate the surface 
of the pond for some time. It can be shown that the wind has 
produced two distinct types of waves. The tiny ripples belong 
to the class known as capillary waves, are like the ripples pro- 
duced by a falling raindrop or a fine wire moved through the 
water, are due to surface tension rather than to gravity, and move 
the more rapidly the smaller the wave length. On the other 
hand, the larger waves on the leeward side of the pond belong 
to the class usually denominated by the term " waves of os- 
cillation," are due entirely to gravity, move the more rapidly 



8 WATER WAVES 

the greater the wave length, and very large examples in the ocean 
may travel for hours or days without any sensible loss of energy 
due to viscosity. There is a certain length of wave, therefore, 
on the border line between large ripples and small waves of 
oscillation, which has the slowest rate of motion. Progressively 
shorter waves travel with increasing velocities and belong to the 
class of ripples. Those of progressively greater length also travel 
with increasing velocities, but belong to the class of true waves of 
oscillation 35 . A good brief summary of the principal points in 
the theory of oscillatory waves will be found in a paper published 
by Lyman in 1868 36 . 

Wave Motion. — In all types of waves, the wave form moves 
far over the surface of the water while the individual water 
particles move but a comparatively short distance; just as 
" waves " may be seen to sweep across a wheat-field with every 
gust of wind, although the individual stalks of wheat merely 
bend slightly and then return to their original positions. The 
contrast between wave movement and water movement is 
strikingly exhibited when waves advance up an estuary during the 
ebbing of the tide. In typical waves of oscillation in deep water 
each water particle moves through a circular orbit, the particle 
moving forward on the crest of the wave, downward on the back, 
backward in the trough, and upward on the wave front. The 
relation of the orbital paths of the water particles to the direction 
of wave propagation is shown in Figure 1. It is important to 
note with care both the direction of orbital motion, and the part 
of the orbit in which a water particle has a given direction, as 
these points frequently are incorrectly represented. For ex- 
ample, one of our best known college texts on " Physiography " 
contains a figure illustrating wave motion which erroneously 
shows the direction of orbital movement at the crest of the wave 
as opposite to the direction of wave propagation, while the 
black dots representing the water particles are in the wrong 
positions in all of the orbits except those showing the particle 
at the top of wave crest and bottom of wave trough. 

A cork or piece of seaweed floating on the water, and moving 
with the water particles, may be seen to describe a circular orbit 
when a wave form passes under it. The cork is at the top of 
its orbit as the crest of a wave passes, reaches the bottom as 
the trough passes, and attains the top. when the next crest 



WAVE MOTION 



arrives. Thus the time re- 
quired for the cork to move 
through its orbit is precisely 
that required for the crest of 
the wave to advance a dis- 
tance equal to one complete 
wave length, i.e., the distance 
from the crest of one wave to 
the crest of the next. Now 
in a wave 20 feet high, having 
a length of 1000 feet or more, 
it is evident that the water 
particle travels through its 
circular orbit a distance of 
but little more than 60 feet ^ 
while the wave form travels 
a fifth of a mile. As we shall 
see in a later paragraph, the 
velocity of waves is often so 
great that the ocean would be 
unnavigable were it not for 
the fortunate fact that the 
water does not travel with 
the wave form. 

Although emphasis is prop- 
erly laid upon the fact that 
the particles of water move 
in a limited orbit while the 
wave form progresses, the 
common statement that in 
the open sea the water parti- 
cles have no progressive mo- 
tion is not quite accurate. 
In 1847 Stokes demonstrated 
from the mathematical stand- 
point that " the particles, in ' 
addition to their motion of 
oscillation, will have a pro- 
gressive motion in the direc- 
tion of propagation of the waves 




" 37 ; the forward motion of the 



10 



WATER WAVES 



particles being not altogether compensated by their backward 
motion. According to Stokes this progressive motion, in deep 
water at least, decreases rapidly as the depth of the particle 
considered increases. Cialdi later discussed this progressive mo- 
tion of the water particles at much length, and sought to ex- 
plain it as in part a consequence of the increase in density of 
the particles brought about by the cooling due to evaporation 
and radiation at the crests of the waves 38 . It is certain that 
the wind by pressing more upon the posterior parts of the waves 
than upon the anterior parts, gives a distinct progressive motion 
to the water involved in oscillatory waves, and that this motion 
is greatest at the surface, decreasing with depth. Stokes has 
developed a formula for calculating the extent to which a ship 
may be drifted from her course by the progressive motion of 
the water particles in waves of this class, although he does not 
regard the formula as of practical importance 39 . 

In water of limited depth the water particles move round 
and round in ellipses whose major axes are horizontal (Fig. 2), 




Fig. 2. — Diagram showing the elliptical orbits of water particles in shallow- 
water waves, and the decrease in size of orbits with increasing depths. 
(After Krummel.) 

and at the bottom the ellipses are reduced to straight lines, the 
water particles simply moving forward and backward 40 . In 
somewhat deeper water the particles near the surface will move 
in circles, those farther down in ellipses, and those on the bottom 
in straight lines. It is this back-and-forth movement on the 
bottom which Emy 41 was considering when he proposed his 
theory of " ground waves " or " bottom waves " (flots de fond), 
although he apparently included in addition certain phenomena 
of waves of translation. This theory was assigned an undue 
importance, and was greatly elaborated by Cialdi 42 and Cor- 
naglia 43 , and by others of the Italian school whose works discuss 
the " flutto di fondo " at much length. The latter' author lays 



WAVE MOTION 



11 



much stress on the existence of a " neutral line " where the land- 
ward and seaward components of the groundwave are supposed 
to be exactly balanced; and considered that inside this line the 
motion of debris is landward, while outside it is seaward. Thou- 
let 44 applies the term " lames de fond " to waves of an entirely 
different type, — waves originating from seismic disturbances, 
"the discussion of which will be taken up on a later page. On 
a level sea-bottom covered by a limited depth of water, it is 
evident that oscillatory waves would cause sand to shift back 
and forth, but would give to it no progressive motion, were 
there no progressive motion of the water particles themselves. 
If we admit the existence of the progressive motion discussed in 
the preceding paragraph as characteristic of normal waves of 
oscillation, it would seem to follow that this motion will still 
obtain when the orbits are reduced to straight lines, and that we 
should therefore expect, in the absence of opposing forces, a slow 
but progressive transfer of sand in the direction of wave advance. 
Caligny investigated a series of waves formed by raising and 
lowering a cylinder in the end of a wooden trough, and found 
that the water particles moved in elliptical orbits which had their 
greatest diameters vertical instead of horizontal. It is possible 
that the orbital motion of this type of wave is responsible for 
those illustrations of sea waves appearing in certain text-books 
of physical geography, in which the orbital paths are shown as 
ellipses, with major axes vertical. But according to Caligny 45 
these waves are peculiar in several respects : they belong to the 
class of waves of translation, although they have an oscillatory 
movement; and experiments showed that grains of sand and 
other material were slowly transported along the bottom of the 
trough in a direction opposite to that of the wave propagation. 
It would seem inadmissible to compare these waves with those 
formed by the wind in the open ocean. Bremontier 46 supposed 
that in normal wave motion the water particles rose and fell in 
vertical paths, while Emy 47 presents arguments to show that 
the paths must be ellipses with the major axes vertical. In 
both cases the arguments are evidently unsound, and the con- 
clusions opposed by the results of more modern studies of deep- 
sea waves. In short, I have not found a satisfactory basis for 
those illustrations of deep-sea waves showing elliptical orbits 
with major axes vertical. 



12 



WATER WAVES 



As will readily appear from Figures 2 and 3 the size of the orbits 
through which the water particles move decreases rapidly with 
increase in depth. At the depth of one wave length below the 
surface, the water particles of an oscillatory wave are moving 
in orbits whose diameters are only 53 \ 5 as great as the diameter 
of the orbits at the surface 48 . We may express this relation in 




Fig. 3. — Diagram showing theoretical form of a cycloidal wave, and the 
rapid decrease in size of the orbits (through which the water particles 
move) with increasing depth. 



the following rule 49 : For each additional J of the wave length 
below the mid-height of the surface wave, the diameter of the 
orbit is decreased by J. Thus : 



Depth below mid-height of surface wave in frac- 
tions of wave length 0, 

Proportionate diameter of orbit 1, 



etc. 
etc. 



For the diameter of an orbit situated one wave length below the 
surface, the rule would give a value of j^ of the surface orbit, 
which is approximately correct and is the figure quoted by 
Cornish 50 and others. If the sea is disturbed by waves having 
a height of 20 feet and a length of 400 feet, the water parti- 
cles at the surface move in circles having a diameter of 20 feet, 
while the particles at a depth of 400 feet move in circles only 
tV of an inch in diameter. The importance of this principle will 
appear when we come to consider the depths at which waves 
may erode the sea-bottom and transport material. 

Wave Form. — The theoretical form of oscillatory waves in 
the open sea is indicated by Figure 4 which represents the profiles 



WAVE FORM 13 

of three such waves. The profiles are trochoidal curves 51 , or the 
curves which would be described by points within a circle which is 
rolled along the under side of a straight line. In the figures 
this curve is produced by drawing a series of circular orbital 




Fig. 4. — Theoretical profiles of three trochoidal waves having different 
sized orbits (solid-line profile and broken-line profile), or different spacing 
of orbits (broken-line profile and dotted-line profile). Modified after 
Grabau. 

paths, indicating the proper position of the water particle in 
each orbit, and connecting these positions by a curved line. As 
will appear from the figures, the sharpness of the wave crests 
varies according as the series of orbits having water particles 
in the same given positions, is closely or widely spaced. From 
the mathematical standpoint, the curve will be sharp crested or 
not according as the point within the rolling circle is at or near 
the circumference, or near its center. If at the circumference, 
the curve developed will be the very sharp crested form called 
the cycloid (Fig. 3). This is the shortest and steepest form 
which a true wave theoretically can have 52 . As a matter of 
fact no wave approximating the form of the common cycloid 
can be produced in nature, as Gaillard has shown 53 . In the 
steepest deep-sea waves observed the ratio of height to length is 
only about one-half that demanded by the cycloidal wave form 54 . 
It is doubtful whether the precise form of the flatter trochoid is 
ever achieved, for it can be shown that the trochoidal theory of 
waves does not adequately satisfy all the conditions of wave 
formation 55 . Nevertheless, the deviation of deep-water waves 
from the true trochoidal form is so slight, and the trochoidal 
theory, especially as modified by Stokes 56 , is so superior to all 
other theories of wave formation, that we shallnot go far wrong 
if we consider such waves as having the form of the trochoid 
and call them trochoidal waves. 

In any trochoidal wave the crest is steeper and narrower 
than the trough and contains an insufficient amount of water 
to fill the trough. The level of the water during calm is there- 
fore lower than the level of the centers of the orbits which the 



14 



WATER WAVES 




WAVE FORM 15 

surface water particles describe during wave action. In other 
words, half the height of the waves does not give the true sea 
level, that level being somewhat lower. Stevenson gives a for- 
mula prepared by Rankine, for calculating the position of mean 
sea level when height and length of wave are known; he also 
observes that large waves in Wick Bay had about two-thirds 
of their height above still-water level, and one-third below 57 . 
On the basis of extensive observations Gaillard has devised 
more satisfactory formulae for determining the still-water level, 
taking due account of the fact that a larger percentage of wave 
height is above still-water level in shallow water than would be 
indicated by a formula which, like Stevenson's, is applicable to 
deep-water waves. Gaillard found that in shallow water about 
three-quarters of the wave height is above still-water level 
just before the wave breaks 58 . The importance of this fact will 
be apparent when it is remembered that the effective salt-water 
level of the sea may thus be raised a number of feet above high 
tide level, and also that floating logs or blocks of ice may accom- 
plish considerable work to any height reached by the crest of 
the waves. 

When a strong wind is blowing, the trochoidal profile of the 
waves is seen to be materially altered. If the wind is in the 
direction of wave propagation, as is more commonly the case in 
the open sea, the forward motion of the water particles on the 
wave crest is accelerated, while the backward motion in the 
trough is retarded. Since the troughs are somewhat protected 
from the wind, the retardation is less effective than the accelera- 
tion of the wave crests. The net result is a steepening of the 
front of the wave, so that the profile becomes noticeably asym- 
metrical. Winds of sufficient velocity may even force some of 
the water on the wave crest out of its orbital path, blowing it 
forward into the adjacent trough in the form of foam and spray. 
When asymmetrical waves pass out of the region of the storm 
winds which generated them, they decrease in height, become 
more rounded and symmetrical, and closely approach the tro- 
choidal form, although the steeper front has been observed on 
deep-water waves in calm weather 59 . These waves may be 
propagated hundreds or thousands of miles from the storm center 
where they originated, and ultimately become the gentle undu- 
lations known as the " swell," or " ground swell." 



16 WATER WAVES 

Surf. — A very important alteration of form occurs when the 
oscillatory wave passes into shallow water. The wave becomes 
higher and shorter, the front steepens, the crest arches forward 
and, finding itself unsupported by sufficient water on the front of 
the wave, dashes downward with a roar, producing the phenom- 
enon known as the " surf." An individual breaking wave is 
known as a " breaker," or less frequently asa" combing wave "; 
the latter term is also applied to a deep-water wave whose crest is 
pushed over forward by a strong wind. The commonly accepted 
explanation of surf is that the wave is retarded by friction when 
it enters shallow water, the lower part " dragging " on the 
bottom while the upper part advances unimpeded, until the wave 
becomes so steep in front that it falls forward. There seem to be 
fatal objections to this theory of surf action. In the first place 
the amount of friction necessary to produce the observed result 
does not seem to exist. Experimental studies of waves in shallow 
water of uniform depth under conditions favorable for the 
development of frictional retardation fail to show it 60 . On the 
other hand, it will later be shown that wave velocity decreases 
with decreasing depth. It is equally certain that the size of 
the orbital paths increases as waves enter shallower water, 
while at the same time the volume of water is decreasing. With 
constantly enlarging orbits and diminishing water supply, there 
must come a time when the volume of water is insufficient to 
build up the entire wave form, the deficiency manifesting itself 
asa" hollowing " of the front of the wave. The water available 
endeavors to curve around through the entire orbit, but on reach- 
ing the top of the circle finds itself unsupported and collapses. 

The form of a breaking wave is not that which should exist 
if friction were the principal cause of the surf. If the observer 
can secure a position where the wave profile is discernible, he 
will find that there is a steepening of the wave front, to be sure, 
but the form does not suggest a steepening due to forward in- 
clination of the whole wave mass resulting from " bottom drag," 
so much as it does a steepening due to the absence of water on, 
and consequent hollowing of the front side of the wave. When 
the wave finally breaks, masses of foam floating on the water 
surface appear to describe an orbit that is more symmetrical 
than one should expect in a wave deformed by great bottom 
friction, while the forward arching crest tries to complete a 



WAVE FORM 



17 




. 



■8 

o 

I 

a 



.a 

o 

of 

03 
bfi 

1 



18 WATER WAVES 

wave form which, if achieved, would not show excessive steepen- 
ing on the front. (Plate II.) The credit for first stating the 
above explanation of surf action belongs to Hagen 61 . 

Depth at Which Waves Break. — The depth of water in which 
the oscillatory wave assumes the form of a breaker is a mat- 
ter of some interest. As in the case of the wave of translation, 
described below, Russell 62 found that breaking occurred when 
the depth of the water equalled the height of the wave, a rule not 
wholly confirmed by the experiments of Bazin 63 , who found that 
breaking occurred more frequently when the height of the wave 
exceeded two-thirds of the total depth. Russell states that his rule 
also holds good for oscillatory waves, but unfortunately he is 
neither clear nor consistent in his method of calculating wave 
height and water depth in the case of these waves. In one place 
we read that " every wave broke exactly when its height above the 
antecedent hollow was equal to the depth of the water," the 
method of calculating water depth not being stated; on another 
page both wave height and water depth are apparently mea- 
sured from mean water level; according to a third statement the 
author never saw a wave as much as 10 feet high in 10 feet of 
water, nor 20 feet high in 20 feet of water, although he has seen 
waves approach very nearly to those limits 64 . Cornish expresses 
the rule as follows: waves break when the depth of water reck- 
oned from the undisturbed sealevel is equal to the height of the 
crest above the trough 65 . In other words, a wave entering 
shallowing water increases in height as the water decreases in 
depth until the height of the wave above the trough, and the mean 
water depth reach approximate equality, when the wave breaks. 
According to this rule the navigator who sees waves 8 or 9 feet 
high (or about 6 feet above still-water level) breaking over a 
certain submarine bar, may know that he can count on but 8 
or 9 feet of mean water depth, or 6 feet of depth below the trough, 
at the place in question. Some other factor or factors, however, 
combine with water depth to determine the breaking of a wave, 
with the result that the above rule does not always hold. De- 
partures from the rule are noted by Stevenson 66 . Cialdi 67 cites 
a great number of cases in which waves have been known to 
break in water many times deeper than the wave height, and 
both Thoulet 68 and Krummel 69 have placed some of these in 
tabular form. The latter author suggests that the frequent 



WAVE FORM 



19 




20 WATER WAVES 

breaking of waves in deep water just above the outer edge of a 
submarine terrace may be due to an upward push imparted to 
the lower water when it comes against the terrace face, this 
push being transmitted to the surface and causing the waves 
to break 70 . Gaillard found that while oscillatory waves some- 
times break quite uniformly when the true height of the wave 
equals the depth of the water measured from still-water level, 
in other cases they break when the ratio of water depth to wave 
height is from 1.16 to 2.71. He observed that the depth at 
which breaking occurs varies with variations in wind velocity, 
slope of bottom, smoothness of bottom, and wave length; and 
suggests that the strength of the undertow is probably another 
important factor in determining the depth at which waves break. 
In addition to his own observation Gaillard quotes those of 
many other observers 71 . The depth of breaking is of importance 
in determining the position of barrier beaches and other related 
shore forms. 

Intersecting Waves. — Thus far we have considered the form of 
waves from the standpoint of changes in profile. If now we turn 
to their variations in form along the crest line, we have first to 
note that the typical oscillatory wave can not be traced far in the 
direction indicated. The~crest soon descends at either end and is 
lost in the maze of other waves. In the open sea one experiences 
the greatest difficulty in determining the end limits of a given 
crest, and also in following the progressing crest for any length 
of time. The reason for this is found in the fact that more than 
one set of waves are always disturbing the ocean surface, and 
the several sets intersect each other at various angles. Even 
with two intersecting series it is evident that the water will 
rise very high where crest coincides with crest, will fall very 
low where trough coincides with trough, and will have all in- 
termediate elevations where different parts of the front and back 
of one wave intersect different parts of another wave. Imagine 
Several series of waves crossing each other at distinctly different 
^ngles, and we have an adequate explanation for all the great 
frregularity in wave form observed in the open ocean. Only 
when the observer is stationed high above the tossing waters, 
and then only under favorable conditions, can he distinguish the 
several orderly systems of waves which are responsible for the 
apparent chaos. 



WAVE HEIGHT 21 

But even in a single wave system the crests are not of in- 
definite extent. This is because the wind which causes the waves 
is never of uniform strength, and because the large waves result 
in part from unequal combinations of smaller waves, as shown on 
a later page. The wind comes in gusts of varying strength and 
somewhat varying direction, and so irregular a force could not 
produce a regular wave crest stretching far over the ocean. 
Instead we have a large number of short, nearly parallel, over- 
lapping crests which in course of time combine into a smaller 
number of larger but decidedly irregular waves. Even in the 
region of the trade winds, where the winds blow with an un- 
usual degree of regularity, " the open sea does not present a 
series of parallel ridges, each one of uniform height, with a lat- 
eral extension many times greater than the distance from crest 
to crest " 72 . On the contrary, there is no evidence of any contin- 
uous approximation toward regularity. 

Wave Height. — In discussing the sizes of waves we have to 
do with two principal elements of wave form : the height measured 
from the bottom of the trough to the top of the crest; and the 
length measured from crest to crest, or from trough to trough. 
The initial height of the oscillatory waves depends on: (1) the 
strength of the wind, (2) its duration, and (3) the extent of open 
water over which it blows. A faint breeze sets in motion very 
small waves which increase in size to a certain limit, but which 
would never become great billows. In the trade wind belt the 
maximum height of wave for a certain strength of wind is soon 
reached, and although the wind may continue steadily for days 
at the given strength, there is no increase in the size of the waves. 
In a general way, the velocity of the wind in statute miles per hour 
divided by 2.05 will give the height of the waves in feet 73 . Thus 
the average height of waves in a gale blowing 44 statute miles per 
hour is 

44 -v- 2.05 = 21.5 feet. 

It should be noted, however, that in very severe storms the 
highest waves may not occur when the wind velocity is at a 
maximum, but are seen to develop as the wind begins to subside. 
The explanation of this phenomenon is probably to be found in 
the fact that the excessive force of a violent wind blows off the 
tops of the waves and casts them into the preceding troughs, 



22 WATER WAVES 

thereby materially diminishing the wave height. It is possible 
also that as the storm subsides the waves, which were com- 
pelled to remain independent and irregular under the gusty force 
of the storm wind, gradually combine into a smaller number of 
larger waves which are little affected by the failing strength of 
the dying wind 74 . 

Effect of Wind Duration. — Wind duration is another factor in 
increasing wave height up to the limiting height for a given wind 
strength. When a breeze springs up, small ripples first appear 
over the water surface, but gradually develop to larger size with- 
out any increase in the strength of the breeze. If a large swell is 
already running in the direction of the wind, a sudden increase in 
wind velocity results in increased height of waves; but in this case 
the wind does not have to endure very long to bring about a very 
remarkable increase in height. Cornish has recorded an increase 
of 7 feet in the height of waves during a squall lasting 4 minutes, 
and an increase of 2 feet per minute in the height of waves during 
another squall 75 . The precise method by which small wind waves 
grow to large ones is not wholly understood, but the Weber 
brothers give the following four causes for wave enlargement: 
(1) the continuous horizontal pressure of the wind upon the 
wave crest, thus tending to enlarge the orbital movement of the 
water particles; (2) the combining of several smaller waves 
moving in the same direction; (3) the pressure exerted by a large 
wave upon the next following smaller wave, by which the latter 
is enlarged ; and (4) the crossing of waves proceeding in different 
directions 76 . Cornish thus states another theory of wave en- 
largement: " The horizontal velocity of the air being greatest 
at the crest, the downward pressure of the atmosphere is least 
there. Conversely at the trough, where horizontal velocity is 
least, downward pressure is greatest. Hence the trough is 
pushed farther down and the crest is sucked up " 77 . 

Effect of Length of Fetch. — Of corresponding importance is the 
effect of " length of fetch " of the wind across open water upon 
wave height. We have already seen that when a breeze blows 
across a pond there first appear small ripples over all its surface 
but that 1 ; these soon increase in size progressively toward the 
leeward side of the pond. The ripples on the windward side, 
where the wind has blown across a small expanse of water only, 
remain small no matter how long or how strong the breeze may 



WAVE HEIGHT 



23 



blow. But those on the leeward side, where the fetch of the 
wind across open water is greater, soon develop into waves of 
some size because here the waves due to the direct effect of the 
wind are combined with the waves originating on the opposite 
side of the pond and propagated by gravity in the direction of the 
wind. This illustrates on a small scale a matter of much impor- 
tance in the case of sea waves. Stevenson has shown that for 
ordinary gales and distances the height of the waves in feet is 
1.5 times the square root of the distance in nautical miles which 
the wind has blown over open water 78 ; or 



height = 1.5 v distance. 

Gaillard observed waves 23 feet high near Duluth with a 
length of fetch of 259 nautical miles 79 . This agrees fairly well 
with the calculated height of 24.1 feet based on the formula. 
Des Bois prepared a table to show the heights of waves corre- 
sponding to different wind velocities, based on his observation 
that a wave 2 meters high corresponded to a wind velocity of 
5 meters per second, and the provisional theory that " the square 
of the velocity of the wind will be proportional to the cube of 
the height of the wave"; and he found that this table corre- 
sponded roughly with the results he obtained from a large number 
of direct measurements 80 . 

For short distances a modification of Stevenson's formula 
is necessary. The following table is condensed from one given 
by that author, and shows the appproximate heights of waves 
as determined by length of fetch, assuming great depth of water 
and a strong gale of wind. 

TABLE SHOWING APPROXIMATE HEIGHTS OF WAVES 
DUE TO DIFFERENT LENGTHS OF FETCH 



Nautical 


Heights 


Nautical 


Heights 


Nautical 


Heights 


miles 


in feet 


miles 


in feet 


miles 


in feet 


1 


3 


5 


4.3 


50 


10.6 


2 


3.4 


10 


5.6 


100 


15 


3 


3.8 


20 


7.1 


200 


21.2 


4 


4.1 


30 
40 


8.4 
9.5 


300 


26 



For expanses of open water exceeding 500 or 600 miles in 
length the height of storm waves does not appear to increase 



24 WATER WAVES 

according to Stevenson's empirical formula. With a fetch of 
3600 miles the waves should reach a height of 90 feet, but so 
great a height is probably never attained. The reason for this 
discrepancy is doubtless to be found in the fact that we have no 
storm winds blowing steadily for a long period in the same di- 
rection over so great a stretch of water 81 . The facts that the wind 
direction may be approximately the same over a long stretch of 
water, or that it may have a constant direction for several days 
at a given place, as noted by Redfield and by Stevenson 82 , are 
not alone sufficient. The winds must blow with the strength 
of a strong gale in a constant direction over the entire distance 
for several days, if the full effect of a 2000 or 3000 mile " fetch" 
is to be realized, since the waves formed to windward must 
have time to travel the long distance to leeward and produce the 
Cumulative effect which results in maximum wave height. In our 
cyclonic storms the greatest distance traversed by heavy winds 
in a reasonably constant direction and for a period of time 
sufficient for large waves to develop, probably does not exceed 
600 or 700 miles. The " effective fetch," therefore, is much 
more limited than the absolute distance across open water; and 
Vaughan Cornish has estimated, from a study of charts illus- 
trating weather conditions in the North Atlantic Ocean for 
nine weeks of exceptionally stormy weather, that the greatest 
effective length of fetch during that period was about 600 nautical 
miles 83 . But while waves formed on greater expanses of open 
water do not reach the heights calculated from the formula 
given above, they do exceed the altitude of about 37 feet cal- 
culated for the greatest effective fetch, because they may com- 
bine with an already existing swell and thereby increase their 
height. 

Recorded Wave Heights. — Observations of the heights of waves 
are often unreliable, but the approximate height under different 
conditions has been pretty well established by a number of compe- 
tent observers. On Lake Superior, waves reach a height of from 20 
to 25 feet 84 ; in the Mediterranean Sea, 25 to 30 feet 85 . Scoresby's 
oft-quoted observations on the North Atlantic give a height of 43 
feet for the largest waves 86 , and Cornish reports waves 43 feet high 
from the same ocean 87 . When two great waves intersect, peaks 
of water may rise momentarily to a height of 50 or even 60 feet 88 . 
Although the North Pacific Ocean has a breadth of open deep sea 



WAVE HEIGHT 25 

much greater than that of the North Atlantic, the waves do not 
appear to reach any greater height 89 ; but in the' Southern Ocean 
waves attain heights of from 45 to 50 feet 90 . White refers to 
trustworthy observations of waves of a single series having 
heights of 44 to 48 feet, and mentions waves formed by the com- 
bination of two or more series said to attain from 58 to 65 feet 91 . 
Gaillard gives an interesting tabulation of the height, length, 
and period of ocean waves recorded by a number of different 
observers, the highest figure for wave height in the table being 
u greater than 50 feet," in the case of a wave photographed by 
Capt. Z. L. Tanner of the U. S. Navy 92 . By means of a barom- 
eter Abercromby measured waves 46 feet high in the Southern 
Ocean, and concluded that some waves certainly attain a height 
of 60 feet 93 . Airy was of the opinion that under no circum- 
stances does the height of an unbroken wave exceed 30 or 40 
feet 94 ; but against this theoretical opinion we may safely accept 
the figures of competent observers, and conclude that waves 
40 feet high are of fairly frequent occurrence in the open ocean, 
while heights of 50 feet or more are rare, but not unknown. 

When these high storm waves run out of the storm area, they 
gradually decrease in altitude, and in the form of swells usually 
do not exceed a height of 15 or 20 feet. By the time they are 
nearmg a distant coast they may have been reduced to heights 
of a few feet on.y, and so have become almost imperceptible. 
Entering shallowing water they seem to awaken to new life, 
crowding closer together and increasing in height until they break. 
At the time of breaking the wave height may be anywhere from 
a few feet up to 25 feet or more. If a wave oomes in contact with 
a vertical wall or cliff the base of which reaches down to deep 
water, the wave is reflected back without breaking. The water 
next the wall moves up and down through a vertical distance 
equal to twice the original height of the wave, as does also the 
water half a wave length from the wall. Similarly, a wave run-- 
ning in a direction parallel to a vertical or steep wall has that 
portion of the wave next the wall notably increased in height 95 . 

Combined Waves. — Waves which appear to belong to the same 
series vary greatly in height. The larger figures given above are for 
individual waves, and in each case the average height for the series 
to which the waves belonged was much less. Thus a wave 40 feet 
high may occur in a series of waves having an average height of 



26 WATER WAVES 

but 20 or 25 feet 96 . This inequality in wave height is probably due 
in considerable part to the fact that what appears to be a single 
series of waves of irregular height is really the combined effect of 
two or more series of waves moving in the same direction, each series 
having different but fairly constant height and length. Figure 5 
from Cornish's work on " Waves" shows, in the third line, the pro- 
file of an apparently irregular series of waves (c) resulting from the 
combination of the two regular series (a and b) shown in the first 
and second lines. By holding the page with the figure nearly on a 
level with the eye, but slightly inclined toward the observer, the 
marked irregularity of the combined series may easily be detected. 




Fig. 5. — Diagram showing how two regular series of waves (a and b) of 
different heights and lengths combine to form an irregular series (c). 

The successive wave heights, in feet, measuring from each crest 
to the next trough, toward the right, are as follows: 22.50, 
37.50, 18.75, 40.00, 27.50. The average wave height for an 
indefinite length of this irregular series will be 30 feet or pre- 
cisely the height of the dominant regular series. It is evident, 
therefore, that an observer might conclude that the sea was 
disturbed by a single series of waves 600 feet long and 30 feet 
in average height, and that the real presence of a swell 20 feet 
high would be undetected. This may explain the fact that 
during a storm at sea the long swell remains invisible, yet be- 
comes noticeable as soon as the shorter storm waves die down 
a little 97 . Gaillard suggests, however, that the waves first made 
by a strong wind are of unstable form and cannot travel far 
without being destroyed and contributing their energy to the 
more stable waves of nearly perfect trochoidal form, the " swell "; 
while Taylor is of the opinion that direct wind action causes the 



WAVE LENGTH 27 

water particles to move in orbits of varying amplitude and 
velocity, producing a confused sea; but that as soon as the 
wind ceases the viscosity of the water tends to make the orbits 
identical, and thus to produce a more uniform system of tro- 
choidal waves 98 . 

The combination of two or more series of waves moving in 
the same direction explains the fact that when waves break upon 
the shore, there is a recurrence, at intervals, of waves of excep- 
tional height. It should be noted, however, that while the 
popular idea that every seventh wave is a big one rests upon a 
basis of- fact, the ratio of wave lengths in the combining series 
is just as likely to make every third, or ninth, or some other 
wave the largest; or if three sets of waves combine, the large 
waves may arrive at irregular intervals. 

Wave Length. — The total energy of a wave has been shown 
to vary nearly as the square of the height and as the first power 
of the length, so that these dimensions may be said to measure 
the capacity of a wave for destruction". Of these two important 
elements of wave form we have just considered the height, and 
may now turn our attention to the length. 

The ratio of wave height to wave length is a matter of con- 
siderable interest. Inasmuch as storm waves usually appear 
higher and steeper than those in a moderate sea, we should 
expect this ratio to increase with increasing roughness of the sea. 
Lieutenant Paris found that in a light sea the ratio of height to 
length is only 1 to 39, in a rough sea 1 to 21, while in a heavy sea 
it rises to 1 to 19 100 . Schott compared the ratios directly with 
the strength of the wind, and found that with a moderate wind 
the ratio of height to length was 1 to 33, with a strong wind 1 
to 18, and with a storm wind 1 to 17 or even as high as 1 to 13 101 . 
On the other hand, White compares the ratios with the lengths 
of the waves, and shows that as the lengths increase the ratios 
diminish. Thus he finds from an analysis of 179 published 
French observations that with a wave length of less than 100 
feet, the average ratio of height to length is 1 to 17; with a 
length of 100-200 feet, the ratio is 1 to 20; with a length of 
200-300 feet, 1 to 25; with a length of 300-400 feet, 1 to 27. For 
greater wave lengths the figures are not wholly in accord with 
the theory, while in waves from 100 to 400 feet long the very 
small ratio of 1 to 50 has been observed 102 . Cornish has com- 



28 WATER WAVES 

pared the lengths of waves with the expanse of open water over 
which the wind blows and finds that " the length of the storm- 
waves is increased when the length of the sheet of water is 
increased, but more slowly " 103 . 

The lengths of deep-water waves are quite definitely related 
to their velocities and to their periods, as will be shown more fully 
on a later page; but we may note here that the wave length 
(in feet) is roughly equal to 5f times the square of the period 
(in seconds). Thus, if waves pass a given point at the rate of 
one in every 4 seconds, the wave length must be approximately 
82 feet; for 

Length = 5§ (period) 2 

= 5i (4)* 

= 82 feet. 

Recorded Wave Lengths. — The greatest trustworthy measurement 
of wave length is that recorded by Capt. Mottez of the French 
Navy, for a wave in the North Atlantic, measuring 2750 feet from 
crest to crest. In the English Channel Cornish observed waves 
whose period indicated a length of 2594 feet 104 . Ross observed a 
wave in the South Atlantic 1920 feet long 105 . The greatest length 
reported by Des Bois is 1640 feet 106 , while Major Leonard Darwin 
found the waves of an exceptionally severe storm in the Southern 
Ocean to be 1200 feet in length 107 . Some of these high figures are 
probably due to the combination of two sets of waves in such a 
manner as to give an abnormally long stretch of low water between 
two crests, for storm waves in the open sea are not usually more 
than 600, and very rarely more than 700 feet long. Scoresby 
found the extreme length of the great storm waves measured by 
him to be 790 feet 108 . Officers on the North Atlantic liners regard 
600 feet as an enormous wave length, although they agree that 
larger lengths are to be found in the Southern Ocean, where in 
one exceptional storm Lieutenant Paris found the greatest aver- 
age length was 771 feet, with not a few waves over 900 feet, and 
several surpassing 1312 feet in length 109 . 

There seems to be little doubt, however, that the swell has 
a length often more than double that of storm waves, and at 
least one of the figures given above, that of 2594 feet for the 
length of waves observed by Cornish, refers to the swell. When 
the swell enters shallow water the velocity and wave length are 



WAVE VELOCITY 29 

diminished, but the period remains the same. Since the period 
bears a definite relation to the length of the waves in deep 
water, it is possible, by counting the number of breakers arriving 
at the shore in a given time, to determine the lengths of the 
waves in the open sea. In this manner it has been established 
that the swell in the open sea must not infrequently have lengths 
of from 1000 to 2000 feet, and occasionally more 110 . Now in 
deep-water waves a great wave length means a great velocity, 
and some authorities doubt whether short storm waves will 
lengthen to form the longer swells, since this would mean that 
the speed of the waves was accelerated after the wind ceased to 
act upon them. Antoine 111 , however, believes that just such 
an acceleration does occur. Others suppose that the waves 
are propagated by gravity at the same rate of speed given 
them by the wind, or even that their velocity suffers a slight 
diminution. Cornish concludes that the longer swells are 
present during storms, but are obscured by the shorter waves 
which are then more prominent 112 . We shall find later that 
the longer waves, while they agitate the surface less than storm 
waves, agitate the deeper waters much more, and have an im- 
portant effect upon the shoreline. 

Wave Velocity. — The velocity of oscillatory waves is a mat- 
ter of considerable interest in various connections. We have 
already observed that the wave form travels at a speed very 
much greater than that of the water particles themselves. Thus, 
a wave 400 feet long and 15 feet high will have a velocity of 
about 45 feet per second, while the surface wator particles will 
move round in their orbits at a speed of but 5J feet per second. 
For ocean waves of large size the wave velocity is apt to be six 
or seven times as great as the orbital velocity ; but it is im- 
possible to give any definite rule for the relations of these two 
elements of wave motion 113 . 

We can correlate the velocity of wave motion with wave 
length more precisely, however, for in deep water the velocity of 
the wave depends on its length, and is proportional to the square 
root of its length 114 . The velocity of any wave whose length is 
known may be calculated approximately by very simple for- 
mulae. Thus, the velocity in miles per hour is equal to the 
square root of 2i times the wave length measured in feet 115 . If 
it is desired to have the result expressed in feet per second, then 



30 WATER WAVES 

the velocity in feet per second is equal to 2\ times the square 
root of the length in feet 116 . According to the first formula a 
wave 100 feet long will have a velocity of 15 miles per hour; 

for 

Velocity = V2J X length 

= V2J X 100 = V225 

= 15 miles per hour. 
• 
Ac:ording to the second formula the same wave will have a 
velocity of 22.5 feet per second; for 



Velocity = 2| Vlength 

= 2J V100 = 2i X 10 
= 22.5 feet per second. 

If we reduce the 15 miles per hour, derived from the first formula, 
to feet per second, we get 22 feet per second, which agrees fairly 
well with the result obtained by the second formula; We may 
also determine the approximate velocity of a wave in feet per 
second by the formula: 



Velocity = V5J X length 

which becomes, in the case of the wave described above, 

Velocity = Vb\ X 100 

= 22f feet per second. 

As Gaillard has pointed out in commenting on the above formula, 
the velocity of a deep-water wave is practically the same as that 
which a body would acquire in falling through a distance equal 
to 8 per cent of the wave length 117 . 

Because of the relations existing between wave velocity, wave 
length, and the period of the waves, we may determine the 
velocity of waves in other ways. Thus the velocity of the wave 
in knots per hour is roughly equal to three times the period (in 
seconds) 118 . Or if we transform the period of the wave into the 
number of waves per minute (wave-frequency), then the velocity 
in feet per minute is equal to the wave length multiplied by the 
frequency. The velocity in miles per hour may be found by 
dividing the frequency into 198 119 . Thus if the wave 100 feet 



WAVE VELOCITY 31 

in length, considered above, have a period of about 4§ seconds, 
then the velocity in knots per hour is roughly 13J, for 
Velocity = 3 X period 

= 3 X 4f 

= 13J knots per hour. 

The velocity of this same wave in feet per minute will be 1333; 

for a period of 4J seconds means a frequency of 13J (60 -f- 4J = 

13§), whence we have the following: 

Velocity = wavelength X frequency 
= 100 X 13J 
= 1333 feet per minute. 

This agrees roughly with the velocities previously obtained, 
since it is equivalent to a speed of 22.2 feet per second. The 
velocity as determined from the frequency alone is 14.85 miles 
per hour; for 

Velocity = 198 -v- frequency 
= 198 ^ 13| 
= 14.85 miles per hour. 

In order to determine the velocity of a set of waves by this last 
method it is only necessary to count the number of times per 
minute some floating object bobs up and down as the waves pass 
under it, or to count the waves as they rise against some fixed 
object. The result is in sufficiently close agreement with the 
velocity of 15 miles per hour determined by a preceding formula. 

The periods of waves are more easily determined than are 
length or velocity, for which reason it is convenient to have 
in tabular form the lengths and velocities of deep-water waves 
corresponding to given periods. The table on the following page, 
taken from White's " Naval Architecture " 120 , covers all waves of 
ordinary size. 

Velocities of Shallow-water Waves. — In the preceding pages we 
have discussed the laws controlling the velocities of deep-water 
waves. Shallow-water waves, or waves whose lengths are great 
compared to the depth of the water, obey different laws. It is 
a well-known fact that such waves move less rapidly than deep- 
water waves, and Gaillard has expressed in tabular form the 
relative velocities of the two types, assuming equal wave lengths, 
but varying depths of water for the shallow-water wave, with a 
minimum depth equal to .05 of the wave length 121 . The velocities 



32 WATER WAVES 

LENGTH AND VELOCITY OF DEEP-WATER WAVES 

(After White.) 







Speed of advance 


Period, seconds 


Length, feet 










Feet per second 


Knots per hour 


1 


5.12 


5.12 


3.03 


2 


20.49 


10.24 


6.07 


3 


46.11 


15.37 


9.10 


4 


81.97 


20.49 


12.14 


5 


128.08 


25.62 


15.17 


6 


184.44 


30.74 


18.21 


7 


251.04 


35.86 


21.24 


8 


327.89 


40.99 


24.28 


9 


414.99 


46.11 


27.31 


10 


512.33 


51.23 


30.35 


11 


619.92 


56.36 


33.38 


12 


737.76 


61.48 


36.42 


13 


865.84 


66.60 


39.45 


14 


1004.17 


71.73 


42.49 


15 


1152.74 


76.85 


45.52 


16 


1311.56 


81.97 


48.56 



of shallow-water waves of this type must be calculated by means 
of a formula less simple than those given for deep-water waves, 
since the formula must be applicable to varying depths of water 
Such a formula, and numerous comparisons of the observed 
velocities of shallow-water waves with the velocities computed 
by the formula, are given in Gaillard's treatise on " Wave 
Action " 122 . When the wave length is more than 1000 times the 
depth of the water, the velocity depends wholly upon the depth 
according to Airy, and is proportional to the square root of the 
depth. The velocity of such a wave is the same as the velocity 
which a body would acquire by falling through a distance equal 
to half the depth of the water 123 . This is the law for the velocity 
of the wave of translation as determined by Russell 124 ; and it 
should be noted that Airy is inclined to regard the wave of 
translation as merely a variety of the wave of oscillation 125 . It 
is also interesting to note that while this law is called Airy's law 
or formula by some, and is named for Russell by others, it was 
really applied by Lagrange to water waves at least as early as 
1788 126 , and is therefore better known as the Lagrange Formula. 
The law does not hold good for very shallow depths, according 
to Caligny 127 ; nor in moving water, according to M oiler 128 . 



WAVES OF TRANSLATION 33 

The waves generated in the ocean by earthquakes and sub- 
marine volcanic explosions have lengths which are great in com- 
parison to the depth of the ocean, and must therefore obey the 
laws controlling the movements of shallow-water waves. If 
we determine the velocity of such a wave, therefore, we should 
be able to secure some idea of the depth of the ocean it traverses. 
This was first done by Bache, who estimated the mean depth of 
the North Pacific Ocean (4200 to 4500 meters) from the veloc- 
ity of a wave produced by the Simoda earthquake in 1854; and 
later others followed his example in the cases of the Iquique 
earthquake and the Krakatoa explosion 129 . The calculations are 
necessarily inaccurate for various reasons, but are nevertheless 
of considerable interest. 



WAVES OF TRANSLATION 

Thus far we have confined our attention to waves of oscil- 
lation, in which the water particles move forward on the crest 
and backward in the trough. There is another type of wave 
which is also of great interest to the student of shorelines, al- 
though its importance is not always appreciated. This is the 
" wave of translation," in which the water particles move for- 
ward as the wave passes, but do not exhibit a compensating 
backward motion. While not important on the open sea, this 
type of wave is extensively developed in the shallow waters 
along all coasts, the waves of oscillation generated in deep water 
frequently becoming more or less completely transformed into 
waves of translation as they approach the shore. 

Form. — The wave of translation was discovered by Russell, 
and described at length by him in his reports to the British Asso- 
ciation 130 . He showed that when a volume of water was suddenly 
added to the still water in a canal, or when a portion of the canal 
water was displaced by suddenly plunging a solid body into it, 
or when the canal water was pushed into a mound by the shoving 
motion of a boat or of a plate held vertically, a single prominent 
wave rolled forward over the canal surface. The entire form of 
this wave rose above the still-water surface of the canal, and 
included no trough such as constitutes part of the wave of oscil- 
lation. A careful examination of the newly discovered wave 
showed that it differed widely from oscillatory waves in other 



34 WATER WAVES 

respects, and that the motion of its water particles made the 
name " wave of translation " appropriate. Let us consider 
briefly the essential characters of this wave, turning our attention 
first to the nature of the movements executed by the water 
particles. 

Motion. — Immediately before and immediately after the pass- 
ing of a wave of translation, the surface of the water and the 
water particles in depth may be quite still. During the passage 
of the wave the surface water particles rise and move forward, 
descending again to the original level, but to an advanced po- 
sition horizontally, where they come to rest. Thus in Figure 6 
the particle a rises, moves forward and descends to the position b. 
Water particles below the surface move forward the same dis- 
tance, but their vertical rise diminishes with increase in depth. 



^^~~^ar 


6 ^^-^ 


g* — 


-"V 



Fig. 6. — Diagram showing movement of water particles in a wave of trans- 
lation. (After Russell.) 

The paths described by the water particles are semi-ellipses 
which have their major axes horizontal and equal, and their 
minor axes progressively shorter as the distance below the sur- 
face increases, until on the bottom the path becomes a straight 
line 131 . It will be seen from the figure that water particles ver- 
tically above each other, as aceg, come to rest in the same 
relative position farther on at bdfh. There is thus a real and 
permanent forward translation of the water itself through a short 
distance, in addition to the forward transmission of the wave 
form through a very great distance. The space through which 
the water particles are moved forward is just large enough to 
contain the volume of water in the wave above still-water level. 
Manifestly there are several points connected with the motion 
of the water particles in waves of translation which will prove of 
importance when we come to discuss the effect of waves upon 
shores. The fact that the water particles advance, but do not 
have a compensating backward motion should result in effective 
transportation of sand and gravel on shallow sea-bottoms in the 
direction of wave propagation, unless other forces prevent. It 



WAVES OF TRANSLATION 35 

is likewise worthy of note that in waves of translation the bottom 
particles move forward just as far as do the surface particles, 
whereas we have already seen that in oscillatory waves the move- 
ment of the water particles dies out rapidly below the surface. 
Evidently waves of translation may profoundly affect the bottom 
to great depths, although this conclusion is subject to the quali- 
fication, subsequently to be discussed, that waves of translation 
traversing water bodies of great depth as compared to the size 
of the waves, tend to be transformed into waves of oscillation. 
We shall see later that only one-half of the energy of an oscil- 
latory wave is transmitted forward with the wave form, whereas 
the total energy of a wave of translation is thus transmitted. 

Wave Length. — The length of the typical wave of translation 
is measured from the point where it begins to rise from the still- 
water level in front to the point where the back slope of the wave 
again merges with still-water level. These points are not easily 
determined with accuracy, but according to Russell the wave 
length thus measured on artificial waves is " equal to about six 
times the depth of the fluid below the plane of repose." The 
height of the wave above the still-water surface may be equal to 
the depth of the fluid in repose, but cannot exceed this measure, 
as the wave breaks whenever the height becomes equal to the 
depth 132 . Actual measurements of wave heights and lengths in 
nature are usually made upon the open sea or in other localities 
favorable to the formation of waves of oscillation ; and while it is 
possible that some of the figures previously given are really those 
for waves of translation, no distinction is usually made by the 
observer, and we lack proper data for the range in size of natural 
waves of translation. 

Velocity. — The velocity of the wave of translation depends upon 
the depth of the water measured from the crest of the wave, and 
varies as the square root of the depth. Otherwise expressed, the 
velocity of the wave is the same as the velocity which a heavy 
body will acquire by falling freely through a distance egual to 
half the depth of the fluid below the wave crest 133 . In the deep 
ocean such waves should have very high velocities, and doubtless 
many of the earthquake waves which traverse the ocean with 
velocities from a few hundred miles to nearly a thousand miles 
an hour 134 are true waves of translation; while the tidal wave 
which has a velocity of from 480 to 660 miles an hour in depths of 



-■"I 



36 WATER WAVES 

between 12,000 and 20,000 feet 135 , is a compound wave having 
some of the characteristics of the wave of translation. In very 
shallow water the velocities of waves of translation must of 
necessity be very low. 

Complexities of Waves of Translation. — According to Caligny the 
waves of translation are not always so simple in character as 
supposed by Russell. The French engineer made a series of ex- 
periments which led him to conclude that there are waves of 
translation in which the water particles describe closed orbits; 
that these orbits may approximate vertical ellipses, but that the 
backward movement of the water particles may slightly exceed 
the forward movement, causing material on the bottom to be 
transported in a direction opposite to that of wave propaga- 
tion; and that a solitary wave of translation may pass through 
a series of oscillatory waves, complicating their form and causing 
them to break. He also pointed out that it is possible to have a 
succession of solitary waves of translation which will resemble 
ordinary waves of oscillation, the spaces between the waves 
resembling troughs so closely as to mislead the observer 136 . 

The investigation of waves of translation in nature is further 
complicated by the fact that notwithstanding Hunt's arguments 
to the contrary 137 , normal waves of oscillation appear to be grad- 
ually transformed into waves of translation when they enter 
water which slowly decreases in depth, and hence all intermediate 
phases between the two types of waves may be encountered. 
When the tops of breakers fall forward, the volume of water thus 
added to the water surface in front produces waves of translation 
which run on shore, mingling with waves of oscillation. If 
waves of translation encounter a cliff or steep shore, they may 
be reflected, the direction of the transport of water particles in 
the reflected wave being seaward. For these and other reasons 
which will presently appear, it may be practically impossible 
to determine the nature of the water movements which are 
affecting the distribution of sand and gravel along a shelving 
coast. 

Such complications should not, however, make us lose sight 
of the importance of waves of translation as agents of shoreline 
changes. Under favorable conditions the operation of these 
waves may easily be observed. Thus, when large swells en- 
counter the seaward margin of a submarine terrace (Fig. 7), 



WAVES OF TRANSLATION 



37 



they break and form smaller waves of trans- 
lation which, on a calm day, may cross the 
shallow water to the shore without deforma- 
tion until they break as a secondary surf on 
the beach. The level water surface between 
any two waves of translation may be seen to 
differ distinctly from the true trough of the 
oscillatory wave in deeper water. Russell ob- 
served a striking example of waves of transla- 
tion, formed in the manner above described, 
on the shore of Dublin Bay, and thus de- 
scribes the phenomena: 

" One of the common sea waves, being of the 
second order (waves of oscillation), approaches 
the shore, consisting as usual of a negative or 
hollow part, and of a positive part elevated 
above the level; .... At length the wave , 
breaks, and the positive part of the wave falls 
forward into the negative part, filling up the 
hollow .... After a wave has first been made 
to break on the shore, it does not cease to 
travel, but if the slope be gentle, and the 
beach shallow and very extended (as it some- 
times is for a mile inwards from the breaking 
point, if the waves be large), the whole inner 
portion of the beach is covered with positive 
waves of the first order (waves of translation), 
from among which all waves of the second 
order have disappeared. This accounts for the 
phenomenon of breakers transporting shingle 
and wreck, and other substances shorewards 
after a certain point." Then referring more 
particularly to the conditions at Dublin Bay, 
he says that the " waves coming, in from the 
deep sea are first broken when they approach 
the shallow beach in the usual way; they give 
off residuary waves, which are positive (waves 
of translation); these are wide asunder from 
each other, are wholly positive (i.e., above 
still- water level), and the spaces between them, 




^< 



38 WATER WAVES 

several times greater than the amplitude of the wave, are per- 
fectly flat; and in this condition they extend over wide areas 
and travel to great distances " 138 . 



EARTHQUAKE AND EXPLOSION WAVES 

In investigations of shoreline changes the student may have 
occasion to refer to another class of waves which are occasionally 
developed upon the ocean, and which are improperly called " tidal 
waves." These are the waves of enormous size and destructive 
energy produced by submarine earthquakes and volcanic explo- 
sions, and for^which Hobbs 139 has suggested adopting the Japanese 
name "tsunamis." They occur at such rare intervals, and oper- 
ate for such a brief period, that they are probably not of great 
importance in modeling the forms of the shore. But inasmuch 
as they temporarily raise the upper limit of salt water far above 
its normal position, and leave behind them records which may 
be mistaken as evidences of a former higher stand of the mean 
sealevel, it is important that we become familiar with the work 
of these waves. 

Nature and Origin of Wave Motion. — A submarine earthquake 
may produce several types of waves. There are first the short and 
quick oscillations which travel toward the surface with the velocity 
of sound in water, and which are felt by overlying vessels as a sharp 
and violent shock, often causing the sailors to believe that the ves- 
sel has struck a reef. Old charts contain many isolated shallows 
and reefs reported by vessels which had really experienced earth- 
quake shocks in deep water. Occasionally such shocks are severe 
enough to hurl the ship out of water, to break off its masts, or even 
to destroy the vessel entirely 140 . Those oscillations are not of the 
type which produce prominent surface waves, however. Other 
groups of waves are produced by the dislocation of the sea-bot- 
tom. While the mechanism of these dislocation waves is not 
well understood, it is probable that the uplifting of a portion of 
the sea-bottom raises a mound of water above the general sur- 
face of the sea, and that the settling back of this water generates 
a great wave of translation which traverses the ocean with high 
velocity. Sometimes several such waves are produced, possibly 
by the disintegration of a former single wave of translation 
after the manner described by Russell for some of his experi- 



EARTHQUAKE AND EXPLOSION WAVES 39 

ments 141 . The sudden settling of a submarine crust block may 
generate a negative wave of translation. On the other hand, the 
behavior of many earthquake waves upon reaching the coast 
suggests that they partake of the characters of oscillatory waves, 
the water particles moving backward in a sort of great trough 
toward the oncoming wave crest. According to Reid the waves 
caused by the same earthquake first appear as a depression of 
the water at some ports, and as an elevation at others; a fact 
which he attempts to explain on the theory that the down- 
dropped block generates a negative wave and the upraised block 
a positive wave 142 . It is possible that the phenomena in question 
may be explained as a result of the different velocities with 
which positive and negative waves are propagated, both having 
resulted from the return of a mass of water raised above the 
general level, in some such manner as that described by Russell 
for his " residuary negative waves " 143 . Our knowledge of earth- 
quake waves is still too meager, however, to enable us to speak 
with assurance on this and other questions concerning their 
behavior. An experimental study of their mode of propa- 
gation will be found in the Weber brothers' " Wellenlehre " 144 , 
a full resume of our present knowledge of the subject in Krum- 
mel's " Ozeanographie " 145 , and a good brief statement in Thou- 
let's " Oceanographie Dynamique " 146 . 

In submarine volcanic explosions there is also produced a 
sharp and powerful shock, corresponding exactly to the first 
mentioned effect of earthquakes. At this time small jets of 
water may be shot into the air; but there soon follows a doming 
or up-swelling of the ocean surface, and finally the whole mass 
of up-raised water may be hurled into the air by the escaping 
gases. The doming of the water, the push exerted by the gases, 
and the back-falling mass of water, all tend to produce waves, 
some of which are waves of translation, and some probably oscil- 
latory or compound waves 147 . Explosion waves and dislocation 
waves cannot be distinguished, and the origin of many of these 
waves, often designated collectively as " earthquake waves," 
remains in doubt. According to Krummel, Rudolph supposed 
that the great wave which overwhelmed Lisbon following the 
earthquake of 1755 was due to a volcanic explosion near the 
Portuguese coast 148 . Most authorities agree that the waves which 
followed the eruption of Krakatoa in 1883 were due directly to 



V 



40 WATER WAVES 

the force of the explosion itself, but some have argued that they 
resulted from the masses of rock falling back into the water 149 . 

On the open sea the heights of earthquake and explosion waves 
quickly diminish, and since the lengths are very great, they soon 
become so low and flat as to be unnoticed by vessels. But 
when they enter shallow water they behave like other waves, 
the height increasing until the wave form breaks to produce a 
gigantic surf. The velocity of these waves is very great, as they 
may travel a distance of 9000 or 10,000 miles in 24 hours, and 
one instance is recorded in which a velocity of 900 miles an hour 
was attained 150 . Their periods range from 15 minutes to one or 
two hours, and by assuming them to be the periods of free waves 
in deep water it has been calculated that the lengths of earth- 
quake and dislocation waves vary from 100 miles to 600 miles or 
more 151 . 

Recorded Heights. — As students of shoreline phenomena we are 
more interested in the height attained by this class of waves when 
they reach the coast. We can better appreciate the truly surpris- 
ing elevations at which they may leave evidences of their former 
presence if we review some of the actual cases of which we have 
authentic records. In the years 358 and 365 A.D., the eastern 
shore of the Mediterranean was visited by great waves which passed 
over islands and low shores, sweeping away buildings and thou- 
sands of people. Boats were left on the roofs of houses in Alexan- 
dria, and others were stranded nearly a mile inland near Modhoni 
where they were later found slowly decaying 1 ". Following the 
Lisbon earthquake in 1755 a wave variously estimated as from 
40 to 60 feet high broke on the coast at Cadiz. The great earth- 
quake at Lima in 1724 was followed by a wave said to have been 
80 feet high and which carried four vessels far inland. In 
August, 1868, an earthquake on the coast of Peru resulted in 
large waves, one of which submerged the mainland 55 feet above 
high-water mark. A United States war vessel was carried a 
quarter of a mile inland at Arica, where it remained until an- 
other great wave carried it still farther inland in 1877. This 
last was the wave caused by the Iquique earthquake, and it is 
said to have varied in height from 20 to 80 feet. An earthquake 
on the island of Hondo, Japan, in 1854 was accompanied by a 
wave which rose 30 feet above the usual level of the water. In 
1896 another disturbance on the same coast generated three 



TIDAL WAVES 41 

waves, the largest of which was 50 feet high on the shore. Ships 
were torn from their anchorage, and one two-masted schooner 
was washed nearly a third of a mile inland. The Messina earth- 
quake of December 28, 1908, produced waves which rose nearly 
30 feet high on some of the adjacent coasts. Following the 
eruption of Krakatoa in 1883 waves of enormous height wrought 
destruction over great distances. On the southern end of 
Sumatra one wave was over 70 feet high, and carried a gunboat 
two miles inland where it was left 30 feet above sealevel. In 
Katimbong the wave rose 80 feet, and on the shallow shore of 
Merak, on the Java coast, reached the enormous height of 115 
to 135 feet 153 . 

It is evident that such great waves must leave many records 
of their presence far above the normal level of the sea. Not 
only large vessels and smaller boats, which readily attract the 
popular attention, but fish and other forms of marine life are 
left stranded far inland and high above the reach of the highest 
tides or greatest storm waves. The bones of whales, and well- 
preserved marine shells occasionally found high above the sea, 
must not too readily be accepted as proof of a very recent uplift- 
of the land. Successive earthquake waves in a given ocean 
may deluge the coasts of all the surrounding continents; and 
we must therefore expect to find driftwood, shells, and bones 
of fish well above sealevel at occasional points on almost any 
shore. 

TIDAL WAVES 

The great periodic motion of the sea known as the tide com- 
bines some of the features of oscillatory waves with others be- 
longing to waves of translation. It has been described by 
Russell as a " compound wave of the first order " (wave of 
translation) having more of the characteristics of waves of this 
order than of oscillatory waves 154 . There is no necessity, however 
of our entering into a discussion of the origin and character of 
the tidal wave, since the only elements of its motion of vital in- 
terest to the student of shore forms are the currents it produces, 
and the height to which it rises; both of which points are con- 
sidered in another part of this volume. 

Wheeler has expressed the belief that the rising and falling 
of the tide is accompanied by the production of " tidal wavelets " 



42 WATER WAVES 

which are not the result of wind action, but are in some way 
genetically related to the tide itself 155 . The explanation of their 
origin which he gives is not wholly satisfactory, and his theory 
seems to be based upon his observation that waves from 6 to 24 
inches in height break upon the beach at the rate of ten to twenty 
a minute " when there is an entire absence of wind or other dis- 
turbing cause." In the absence of sufficient evidence to connect 
such wavelets with the tides, we may perhaps more safely regard 
them as due to the action of gentle breezes and occasional gusts 
of wind, possibly some distance away, which even on the calmest 
day never permit the ocean surface to become absolutely quies- 
cent. Haupt 156 states that the flood tide produces waves which 
break obliquely on the beach, and speaks of " the angle at which 
the flood breaks upon the shore." But since he also speaks of 
these supposed tidal waves as " breakers racing along the shore," 
and quotes Mitchell's description of the manner in which the 
" larger class of swell or rollers " strike the shore as an example 
of tidal wave activity, it would appear that Haupt has mistaken 
the ground-swell of distant storms for tidal waves. A similar 
misapprehension may have been responsible for Marsh's curious 
idea that " on most coasts the supply of sand for the formation 
of dunes is derived from tidal waves," since " the momentum 
acquired by the heavy particles in rolling in with the water 
tends to carry them even beyond the flow of the waves " 157 . 



STANDING WAVES; SEICHES 

Under certain conditions there may exist oscillations of the 
water known as standing waves, in which the water particles 
do not describe closed orbits, but return through the same paths 
by which they advance (Fig. 8). The surface water moves up- 
ward in all of the crest, and downward in all of the trough, 
and the vertical movement of the particles is at a maximum 
under the crest where the horizontal movement is nil 158 . Hori- 
zontal movement is at a maximum under the nodal lines (Fig. 8). 
An example of the standing wave is the seiche, typically developed 
in inland lakes, and extensively studied in Lake Geneva by 
Forel. This movement consists of a periodic rise and fall of 
the water surface which is initiated by winds piling up the water 
at one end of the lake, by sudden variations in atmospheric 



STANDING WAVES; SEICHES 43 

pressure, by earthquakes, by landslides, or by some other dis- 
turbance; and which continues for some time with gradually 
diminishing intensity. Each body of water has its own period, 
appropriate to its dimensions, and the extent to which the water 
rises and falls depends on the dimensions of the water body and 
the nature of the disturbing force. The principal seiche on 
Lake Geneva has an amplitude of from 8 centimeters to 2 meters 159 . 




// v\ 




Fig. 8. — Diagram to illustrate the movement of water particles in standing 
waves, such as the seiche. 

Seiches also occur along the coasts of the ocean, especially in 
bays and straits. Examples of these and other types of seiches 
are described in Harris's " Manual of Tides " 16 °, and Thoulet's 
" Oceanographie Dynamique " 161 . According to Dawson 162 a 
seiche at Yarmouth, Nova Scotia, had an amplitude of from 128 
to 143 centimeters, or a maximum change of level of nearly 5 
feet. As a rule, however, most seiches have an amplitude of a 
few inches only. The period varies from a few minutes in small 
water bodies to many hours in large ones, and the velocity of 
the water particles participating in the oscillation is not great. 
Indeed, the direct effect of seiches upon shoreline processes is 
probably almost negligible. In the rare cases where the am- 
plitude is great the effect of seiches is temporarily to raise the 
zone of ordinary wave activity to an appreciable extent; and 
occasionally the rising and falling of the water will cause currents 
of some importance through narrow straits or inlets; but these 
are exceptional cases and do not justify us in devoting further 
space to the subject of seiches in this connection. A good ac- 
count of this type of wave motion, with a short bibliography, 
will be found in the work by Harris already referred to, while 
Darwin's volume on "Tides and Kindred Phenomena" gives 
a description of Forel's important researches and a list of his 
classic papers 163 . 



44 



WATER WAVES 




BOUNDARY WAVES 

Where a layer of lighter surface water overlies a heavier 
water stratum, any sudden wind which creates or accelerates 
movement of the surface water will cause a rise of the under- 
lying heavier water at the point affected, and a corresponding 
depression in the 
heavier water farther 
forward. The de- 
velopment of such 
" boundary waves " 
at the plane of con- 
tact of two liquids Fig. 9. — Boundary wave formed by local air 
having different den- current over liquids of different densities. 

... i-i i (After Sandstrom.) 

sities can readily be 

demonstrated by repeating Sandstrom's experiment, in which one 
of the layers was colored in order to distinguish it from the other, 
and a local air current was artificially generated 164 . (Fig. 9.) 

When fresh water from some large river flows out over the 
heavier salt water of the sea, conditions favoring the formation 
of boundary waves exist. Such waves move very slowly, their 
velocities depending upon the difference in density of the two 

water layers and in- 
creasing with the 
square root of this 
difference 165 . If the 
generating wind 
cease, the boundary 
waves advance to 
the margins of the 
containing basin, 
where they are par- 
tially destroyed and 
partly reflected back 
beneath the surface. 




Fig. 10. — Diagram showing movement of water 
particles in overlying fresh water (white) and 
underlying salt water (shaded) during the 
passage of boundary waves from left to right 
(long arrow). (After V. W. Ekman.) 



In their progress they give rise to surface waves of the same 
length, but much smaller height, the crests of the surface waves 
being directly above the troughs of the boundary waves 166 . Since 
boundary waves have a low velocity, and the water particles 
involved move still more slowly, it may be doubted whether they 



RESUME 45 

are of importance in shore processes. A good brief summary of 
the character of these waves is published by Helland-Hansen 
and Nansen in their report on the Norwegian Sea 167 , while the 
mathematical theory applicable to them has been developed by 

Stokes 168 . 

RESUME 

In the foregoing pages we have gained some idea of the nature 
of that force which is the most important agent in the modeling 
of shore forms. We have considered the form and charac- 
teristics of waves on the deep sea in order that we might the 
better appreciate the changes which they undergo as they 
approach the coast and begin their geological work. The mo- 
tion of the water particles in different types of waves; the nature 
of wave motion in deep water and over shallow sea-bottoms; 
the origin of storm waves, swells, and surf; the magnitude of 
waves and the conditions which govern their size; and the 
velocity of wave advance in both deep and shallow water, have 
in turn received our attention. With these points in mind we 
are prepared to enquire into the energy expended by waves 
upon the shore, and the work thereby accomplished. 

In spite of the apparently hopeless chaos presented by the 
surface of a stormy sea, we know that the waves are controlled 
by definite natural laws, and that the different elements of form 
and motion are in systematic relation to one another. So per- 
fect is this relationship that one may stand upon the beach and 
time the breakers as they dash themselves to pieces at his feet, 
and learn thereby the length and velocity which these same 
waves had, hours ago, far away upon the deep sea. On the 
other hand, we know that not all the laws which control the 
behavior of waves have been discovered; and we have seen 
that where different types of waves act simultaneously upon 
the same water body it may be difficult or even impossible to 
analyze the resultant movements of the water. We are there- 
fore prepared to find that through the work of waves upon a 
coast the shoreline is changed according to definite natural 
laws which are in part, at least, discoverable. But we shall not 
be surprised if, in the present state of our knowledge of waves, 
we find it impossible to explain all of the changes which take 
place upon a shore under their influence. 



46 WATER WAVES 

REFERENCES 
1. Kelvin, Lord (Sir William Thompson). Popular Lectures and Ad- 
dresses. Ill, Navigation, 511 pp., London, 1891. 
> 2. Fleming, J. A. Waves and Ripples in Water, Air, and iEther. 299 

pp., London, 1902. 
» 3. Cornish, Vaughan. Waves of the Sea and Other Water Waves. 
374 pp., Chicago, 1911. 

4. Fleming, J. A. Waves and Ripples in Water, Air, and iEther. 299 pp., 

London, 1902. 

5. Russell, J. Scott. Report on Waves, made to the Meetings in 1842 

and 1843. 

Report of the British Association. XIV, 375-381, 1844 (1845). 

6. Russell, J. Scott. Report of the Committee on Waves, appointed by 

the British Association at Bristol in 1836, etc. 

Report of the British Association. VII, 417-496, 1837 (1838). 
Russell, J. Scott. Report on Waves, made to the Meetings in 1842 
and 1843. 
Report of the British Association. XIV, 311-390, 1844 (1845). 

7. Cornish, Vaughan. Waves of the Sea and Other Water Waves. 

374 pp., Chicago, 1911. 

8. Airy, G. B. On Tides and Waves. Encyclopaedia Metropolitana. V, 

345*-350,* 1848. 

9. Russell,* J. Scott. Report on Waves, made to the Meetings in 1842 

and 1843. 

Report of the British Association. XIV, 337, 1844 (1845). 

10. Krummel, Otto. Handbuch der Ozeanographie. II, Die Bewegungs- 

formen des Meeres, p. 12, Stuttgart, 1911. 

11. Bremontier, N. T. Recherches sur le Mouvement des Ondes. 122 

pp., Paris, 1809. 

12. Weber, Ernst Heinrich and Wilhelm. Wellenlehre auf Experi- 

mente Gegrundet. 433 pp., Leipzig, 1825. 

13. Emy, A. R. Du Mouvement des Ondes et des Travaux Hydrauliques 

Maritimes. 188 pp., Paris, 1831. 

14. Russell, J. Scott. Report of the Committee on Waves, appointed by 
■ the British Association at Bristol in 1836, etc. 

Report of the British Association. VII, 417-496, 1837 (1838). 
Russell, J. Scott. Report on Waves, made to the Meetings in 1842 
and 1843. 
Report of the British Association. XIV, 311-390, 1844 (1845). 

15. Russell, J. Scott. The Modern System of Naval Architecture. 3 

Vols., London, 1865. 

t 16. Bazin, Henri. Recherches Experimentales sur la Propagation des 
Ondes. M6m. de l'Acad. des Sciences de PInst. de France XIX, 
495-644, 1865. 

i 17. Airy, G. B. On Tides and Waves. Encyclopaedia Metropolitana. 
V, 241*-396,* 1848. 
18. Stokes, George Gabriel. Report on Recent Researches in Hydro- 
dynamics. Mathematical and Physical Papers. I, 157-187, 1880. 



REFERENCES 47 

Stokes, George Gabriel. On the Theory of Oscillatory Waves. 

Mathematical and Physical Papers. I, 197-229, 1880. 
< 19. Rankin, W. J. M. On the Exact Form of Waves near the Surface of 

Deep Water. Philosophical Transactions of the Royal Society of 

London. CLIII, Pt. I, 127-138, 1863. 
» 20. Boussinesq, J. Essai sur la Theorie des Eaux Courantes. Mem. de 

l'Acad. des Sciences de lTnst. de France. XXIII, 1-680, 1877; XXIV, 

No. 2, 1-64, 1887. 

21. Bertin, Emile. Etude sur la Houle et le Roulis. Memoires de la 

Societe Imperiale des Sciences Naturelles de Cherbourg. XV, 5-44, 
313-355, 1869. 

22. Bertin, Emile. Donnees Theoriques et Experimentales sur les Vagues 

et le Roulis. Memoires de la Societe Nationale des Sciences Natu- 
relles de Cherbourg. XVII, 209-352, 1873; XVIII, 1-128, 1874; 
XXII, 161-227, 1879. 

23. Saint-Venant, Barre de. Du Roulis sur Mer Houleuse. Memoires/Ie 

la Societe Nationale des Sciences Naturelles de Cherbourg. XVI, 
5-66, 1871. 

24. Mottez, A. Du Courant Alternatif dans la Houle. Memoires de la 

Societe Nationale des Sciences Naturelles de Cherbourg. XVI, 
360-370, 1872. 

25. Cialdi, Alessandro. Sul Moto Ondoso del Mare e su le Correnti di 

esso. 695 pp., Rome, 1866. 

26. Caligny, A. de. Oscillations de l'Eau. 964 pp., Paris, 1883. 

\ 27. Stevenson, Thomas. The Design and Construction of Harbours. 

3rd Edition. 355 pp., Edinburgh, 1886. 
v 28. Fleming, J. A. Waves and Ripples in Water, Air, and iEther. 299 

pp., London, 1902. 
1 29. Wheeler, W. H. A Practical Manual of Tides and Waves. 201 pp., 

London, 1906. 
Q 30. Wheeler, W. H. The Sea Coast: Destruction: Littoral Drift: Pro- 
tection. 361 pp., London, 1902. 
* 31. Cornish, Vaughan. Waves of the Sea and Other Water Waves. 
374 pp., Chicago, 1911. 
32. Krummel, Otto. Handbuch der Ozeanographie. II. Die . Bewe- 
gungsformen des Meeres. 766 pp., Stuttgart, 1911. 
! 33. Gaillard, D. D., Wave Action in Relation to Engineering Struc- 
tures. Corps of Engineers U. S. Army, Professional Paper No. 31. 
232 pp., Washington, 1904. 
» 34. White, W. H. Manual of Naval Architecture. 5th Edition, 731 pp., 
London, 1900. 
35 Kelvin, Lord (Sir William Thompson). Popular Lectures and Ad- 
dresses. Ill, Navigation, p. 456, London, 1891. 
f Fleming, J. A. Waves and Ripples in Water, Air, and iEther, p/42, 
London, 1902. 
Russell, J. Scott. Report on Waves, made to the Meetings in 1842 
and 1843. 

Report of the British Association. XIV, 375, 1844 (1845). 



48 WATER WAVES 

\ 36. Lyman, C. S. A New Form of Wave Apparatus. Jour, of the Frank- 
lin Institute. LXXXVI, 187-194, 1868. 

37. Stokes, George Gabriel. On the Theory of Oscillatory Waves. 

Mathematical and Physical Papers. I, 198, 208, 1880. 

38. Cialdi, Alessandro. Sul Moto Ondoso del Mare e su le Correnti di 

esso, p. 68, Rome, 1866. 

39. Stokes, George Gabriel. On the Theory of Oscillatory Waves. 

Mathematical and Physical Papers. I, 209, 1880. 

40. Stokes, George Gabriel. Report on Recent Researches in Hydro- 

dynamics. Mathematical and Physical Papers. I, 164-165, 1880. 
x 41. Emy, A. R. Du Mouvement des Ondes et des Travaux Hydrauliques 
Maritimes, p. 49, Paris, 1831. 
42. Cialdi, Alessandro. Sul Moto Ondoso del Mare e su le Correnti di 
esso. 695 pp., Rome, 1866. 
x 43. Cornaglia, P. Sul Regime delle Spiagge e sulla Regolazione dei Porti. 
569 pp., Turin, 1891. 
Review, Nature, XLV, 362, 1892. 

44. Thoulet, J. Oceanographie Dynamique, p. 54, Paris, 1896. 

45. Caligny, A. de. Oscillations de l'Eau, pp. 195-197, Paris, 1883. 

46. Bremontier, N. T. Recherches sur le Mouvement des Ondes. 122 

pp., Paris, 1809. 

* 47. Emy, A. R. Du Mouvement des Ondes et des Travaux Hydrauliques 

Maritimes, p. 17, Paris, 1831. 

* 48. Airy, G. B. On Tides and Waves. Encyclopaedia Metropolitana. 

V, 294, 1848. 
Fleming, J. A. Waves and Ripples in Water, Air, and iEther, p. 11, 
London, 1902. 

49 White, W. H. Manual of Naval Architecture. 5th Edition, p. 199, 

London, 1900. 

50. Cornish, Vaughan. Waves of the Sea and Other Water Waves, 

p. 142, Chicago, 1911. 

51. Rankin, W. J. M. On the Exact Form of Waves near the Surface of 

Deep Water. Philosophical Transactions of the Royal Society of 
London. CLIII, Pt. I, 127, 1863. 

52. Fenneman, N. M. Development of the Profile of Equilibrium of the 

Subaqueous Shore Terrace. Jour, of Geol. X, 4, 1902. 

53. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 

Corps of Engineers U. S. Army, Professional Paper No. 31, pp. 55, 
123, Washington, 1904. 

54. White, W. H. Manual of Naval Architecture. 5th. Edition, p. 213, 

London, 1900. 

55. Gaillard, D. D. Wave Action in Relation to Engineering Struc- 

tures. Corps of Engineers U. S. Army, Professional Paper No. 31, 
pp. 36, 55, Washington, 1904. 

56. Stokes, George Gabriel. On the Theory of Oscillatory Waves. 

Mathematical and Physical Papers. I, 197-229, 1880. 
* 57. Stevenson, Thomas. The Design and Construction of Harbours. 
3rd edition, pp. 78, 79, Edinburgh, 1886. 



REFERENCES 49 

i 58. Gaillaed, D. D. Wave Action in Relation to Engineering Structures. 

Corps of Engineers U. _S. Army, Professional Paper No. 31, pp. 

110-114, Washington, 1904. 
\ 59. Cornish, Vaughan. Waves of the Sea and Other Water Waves, p. 135, 

Chicago, 1911. 

60. Krummel, Otto. Handbuch der Ozeanographie. II, Die Bewegungs- 

formen des Meeres, p. 112, Stuttgart, 1911. 

61. Hagen, G. Handbuch der Wasserbaukunst. 3. Teil. Das Meer. I, 

pp. 19, 86, Berlin, 1863. 

62. Russell, J. Scott. Report on Waves, made to the Meetings in 1842 

and 1843. 

Report of the British Association. XIV, 371, 1844 (1845). 
y 63. Bazin, Henri. Recherches Experimentales sur la Propagation' des Ondes. 
Mem. de l'Acad. des Sciences de l'Inst. de France. XIX, 518, 1865. 
64. Russell, J. Scott. Report of the Committee on Waves, appointed 
by the British Association at Bristol in 1836, etc. 

Report of the British Association. VII, 451, 1837 (1839). 
Russell, J. Scott. Report on Waves, made to the Meetings in 1842 
and 1843. 

Report of the British Association. XIV, 371, 1844 (1845). 
x 65. Cornish, Vaughan. Waves of the Sea and Other Water Waves, p. 

170, Chicago, 1911. 
v 66. Stevenson, Thomas. The Design and Construction of Harbours. 
3rd Edition, pp. 77-78, Edinburgh, 1886. 

67. Cialdi, Alessandro. Sul Moto Ondoso del Mare e su le Correnti di 

esso, pp. 145-157, Rome, 1866. 

68. Thoulet, J. Oceanographie Dynamique, p. 51, Paris, 1896. 

69. Krummel, Otto. Handbuch der Ozeanographie. II. Die Bewegungs- 

forem des Meeres, p. Ill, Stuttgart, 1911. 

70. Ibid., p. 112. 

s 71. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 

Corps of Engineers U. S. Army, Professional Paper No. 31, pp. 

114-123, Washington, 1904. 
» 72. Cornish, Vaughan. Waves of the Sea and Other Water Waves, pp. 

132, 133, Chicago, 1911. 
73. Ibid., pp. Ill, 133. 

Cornish, Vaughan. On the Dimensions of Deep Sea Waves, and 

their Relations to Meteorological and Geographical Conditions. 

Geographical Jour. XXIII, 643, London, 1904. 
v 74. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 

Corps of Engineers U. S. Army, Professional Paper No. 31, p. 67, 

Washington, 1904. 
i 75. Cornish, Vaughan. Waves of the Sea and Other Water Waves, pp. 

128, 129, Chicago, 1911. 
76. Weber, Ernst Heinrich and Wilhelm. Wellenlehre auf Experi- 

mente Gegriindet, p. 25, Leipzig, 1825. 
v 77. Cornish, Vaughan. Waves of the Sea and Other Water Waves, 

p. 106, Chicago, 1911. 



50 WATER WAVES 

78. Stevenson, Thomas. The Design and Construction of Harbours. 
3rd Edition, p. 29, Edinburgh, 1886. 
) 79. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 
Corps of Engineers U. S. Army, Professional Paper No. 31, p. 69, 
Washington, 1904. 

80. Bois, Coupvent des. Memoire sur la Hauteur des Vagues a la Sur- 

face des Oceans. Comptes Rendus de l'Acad. des Sciences. LXII, 
pp. 86-87, 1866. 

81. Cornish, Vaughan. On the Dimensions of Deep Sea Waves, and 

their Relations to Meteorological and Geographical Conditions. 

Geographical Jour. XXIII, 636, London, 1904. 
N 82. Stevenson, Thomas. The Design and Construction of Harbours. 

3rd Edition, pp. 34, 35, Edinburgh, 1886. 
> 83. Cornish, Vaughan. Waves of the Sea and Other Water Waves, p. 

67, Chicago, 1911. 

84. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 

Corps of Engineers U. S. Army, Professional Paper No. 31, p. 82, 
Washington, 1904. 

85. Cornish, Vaughan. Waves of the Sea and Other Water Waves, 

pp. 33, 40, Chicago, 1911. 

86. Scoresby, William. On Atlantic Waves, their Magnitude, Velocity, 

and Phenomena. 

Report of British Association for 1850, Pt. II, p. 28, 1851. 

87. Cornish, Vaughan. Waves of the Sea and Other Water Waves, pp. 

53, 60, Chicago, 1911. 

88. Scoresby, William. On Atlantic Waves, their Magnitude, Velocity, 

and Phenomena. Report of British Association for 1850, Pt. II, 
p. 28, 1851. 
'• Cornish, Vaughan. Waves of the Sea and Other Water Waves, 
p. 60, Chicago, 1911. 
Cornish, Vaughan. On the Dimensions of Deep Sea Waves, and 
their Relations to Meteorological and Geographical Conditions. 
Geographical Jour. XXIII, 627, London, 1904. 

89. Cornish, Vaughan. Waves of the Sea and Other Water Waves, ,p. 

62, Chicago, 1911. 

90. Ibid., pp. 74-77. 

91. White, W. H. Manual of Naval Architecture. 5th Edition, p. 212, 

London, 1900. 

92. Gaillard, D. D. Wave Action in Relation to Engineering Struc- 

tures. Corps of Engineers U. S. Army, Professional Paper No. 31, 
pp. 76-79, Washington, 1904. 
1 93. Abercromby, Ralph. Observations on the Height, Length, and Ve- 
locity of Ocean Waves. Philosophical Magazine, XXV, 269, 1888. 

94. Airy, G. B. On Tides and Waves. Encyclopaedia Metropolitana, 

V, 351, 1848. 

95. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 

Corps of Engineers U. S. Army, Professional Paper No. 31, p. 85, 
Washington, 1904. 



REFERENCES 51 

96. Cornish, Vaughan. On the Dimensions of Deep Sea Waves, and 

their Relations to Meteorological and Geographical Conditions. Geo- 
graphical Jour. XXIII, 626, London, 1904. 

97. Cornish, Vaughan. Waves of the Sea and Other Water Waves, pp. 

96-101, Chicago, 1911. 
Cornish, Vaughan. On the Dimensions of Deep Sea Waves, and their 
Relations to Meteorological and Geographical Conditions. Geographi- 
cal Jour. XXIII, 627-633, London, 1904. 
* 98. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 
Corps of Engineers U. S. Army, Professional Paper No. 31, p. 57, 
Washington, 1904. 
99. Ibid., p. 70. 

100. Paris, A. Observations~sur l'Etat de la Mer Recueillies a bord du 

Dupleix et de la Minerve (1867-70). Revue Maritime et Coloniale. 
XXXI, 121, 1871. 

101. Schott, Gerhard. Uber die Dimensionen der Meereswellen. Fest- 

schrift Ferdinand Freiherrn von Richthofen zum Sechzigsten Geburts- 
tag, p. 250, Berlin, 1893. 

102. White, W. H. Manual of Naval Architecture. 5th Edition, pp. 

213-214, London, 1900. 
I 103. Cornish, Vaughan. Waves of the Sea and Other Water Waves, pp. 
30, 34, Chicago, 1911. 

104. Ibid., p. 92. 

105. White, W. H. Manual of Naval Architecture. 5th Edition, p. 211, 

London, 1900. 

106. Bois, Coupvent des. Memoire sur la Hauteur des Vagues a la Surface 

des Oceans. Comptes Rendus de l'Acad. des Sciences. LXII, p. 83, 

1866. 
\ 107. Cornish, Vaughan. Waves of the Sea and Other Water Waves, p. 

73, Chicago, 1911. 
108. Scoresby, William. On Atlantic Waves, their Magnitude, Velocity, 

and Phenomena. Report of British Association for 1850. Pt. II, 

29, 1851. 
\ 109. Cornish, Vaughan. Waves of the Sea and Other Water Waves, 

pp. 70, 82, Chicago, 1911. 

110. Ibid., pp. 88-94. 

Cornish, Vaughan. On the Dimensions of Deep Sea Waves, and their 
Relations to Meteorological and Geographical Conditions. Geo- 
graphical Jour. XXIII, 627, London, 1904. 

111. Antoine, Ch. Des Lames de Haute Mer, p. 3, Paris, 1879. 

) 112. Cornish, Vaughan. Waves of the Sea and Other Water Waves, p. 87, 

Chicago, 1911. 
113. White, W. H. Manual of Naval Architecture. 5th Edition, p. 205, 

London, 1900. 
N 114. Airy, G. B. On Tides and Waves. Encyclopedia Metropolitana. 

V, 292, 1848. 
\ 115. Fleming, J. A. Waves and Ripples in Water, Air, and iEther, p. 10, 

London, 1902. 



52 WATER WAVES 

116. White, W. H. Manual of Naval Architecture. 5th Edition, p. 204, 
London, 1900. 
\ 117. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 
Corps of Engineers U. S. Army, Professional Paper No. 31, p. 38, 
Washington, 1904. 

118. White, W. H. Manual of Naval Architecture. 5th Edition, p. 204, 

London, 1900. 

119. Fleming, J. A. Waves and Ripples in Water, Air, and iEther, p. 11, 

London, 1902. 

120. White, W. H. Manual of Naval Architecture. 5th Edition, p. 205, 

London, 1900. 
' 121. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 
Corps of Engineers U. S. Army, Professional Paper No. 31, p. 44, 
Washington, 1904. 
122. Ibid., pp. 97-103. 
\ 123. Airy, G. B. On Tides and Waves. Encyclopedia Metropolitana. V, 
292, 1848. 
124. Russell, J. Scott. Report on Waves made to the Meetings in 1842 
and 1843. 

Report of the British Association. XIV, 325, 1844 (1845). 
\ 125. Airy, G. B. On Tides and Waves. Encyclopedia Metropolitana. 
V, 346, 1848. 
126. Lagrange. Mechanique Analitique, p. 491, Paris, 1788. 
• 127. Caligny, A. de. Oscillations de PEau, p. 199, Paris, 1883. 

128. Krummel, Otto. Handbuch der Ozeanographie. II. Die Bewe- 

gungsformen des Meeres, p. 29, Stuttgart, 1911. 

129. Ibid., p. 152. 

130. Russell, J. Scott. Report of the Committee on Waves, appointed 

by the British Association at Bristol in 1836, etc. 

Report of the British Association. VII, 417-496, 1837 (1838). 
Russell, J. Scott. Report on Waves, made to the Meetings in 1842 
and 1843. 

Report of the British Association. XIV, 311-390, 1844 (1845). 

131. Russell, J. Scott. Report on Waves, made to the Meetings in 1842 

and 1843. 

Report of the British Association. XIV, 340-347, 1844 (1845). 

132. Ibid., pp. 340, 354. 

133. Ibid., pp. 325-328. 

134. Krummel, Otto. Handbuch der Ozeanographie. II. Die Bewegungs- 

formen des Meeres, pp. 149-150, Stuttgart, 1911. 
Wheeler, W. H. A Practical Manual of Tides and Waves, p. 131, 
London, 1906. 
135 Wheeler, W. H. A Practical Manual of Tides and Waves, p. 57, 
London, 1906. 

136. Caligny, A. de. Oscillations de l'Eau, pp. 191-211, Paris, 1883. 

137. Hunt, A. R. On the Action of Waves on Sea-Beaches and Sea-Bot- 

toms. Proc. Roy. Dublin Soc, N. S. IV, 251-259, 1884. 



REFERENCES 53 

138. Russell, J. Scott. Report on Waves, made to the Meetings in 1842 

and 1843. 

Report of the British Association. XIV, 372-373, 1844 (1845). 

139. Hobbs, Wm. H. Origin of Ocean Basins in the Light of the New Seis- 

mology. Bull. Geol. Soc. Amer. XVIII, 242, 1907, 

140. Krummel, Otto. Handbuch der Ozeanographie. II, Die Bewegungs- 

formen des Meeres, p. 133, Stuttgart, 1911. 

141. Russell, J. Scott. Report on Waves, made to the Meetings in 1842 

and 1843. 

Report of the British Association. XIV, 323, 1844 (1845). 

142. Reid, H. F. Earthquake Sea Waves. Unpublished paper read at 

Princeton Meeting of Geological Society of America. December, 
1913. 

143. Russell, J. Scott. Report on Waves, made to the Meetings in 1842 

and 1843. 

Report of the British Association. XIV, 323, 1844 (1845). 

144. Weber, Ernst Heinrich and Wilhelm. Wellenlehre auf Experi- 

mente Gegriindet. 433 pp., Leipzig, 1825. 

145. Krummel, Otto. Handbuch der Ozeanographie. II. Die Bewegungs- 

formen des Meeres. 766 pp., Stuttgart, 1911. 

146. Thoulet, J. Oceanographie Dynamique. 131 pp., Paris, 1896. 

147. Krummel, Otto. Handbuch der Ozeanographie. II. Die Bewe- 

gungsformen des Meeres, pp. 136-137, Stuttgart, 1911. 

148. Ibid., p. 141. 

149. Ibid., p. 148. 

150. Ibid., p. 149. ' 

v Wheeler, W. H. A Practical Manual of Tides and Waves, p. 131, 
London, 1906. 

151. Krummel, Otto. Handbuch der Ozeanographie. II. Die Bewegungs- 

formen des Meeres, p. 149, Stuttgart, 1911. 

152. Ibid., p. 139. 

153. Ibid., p. 148. 

\ Gaillard, D. D. Wave Action in Relation to Engineering Structures. 
Corps of Engineers U. S. Army, Professional Paper No. 31, p. 91, 
Washington, 1904. 

154. Russell, J. Scott. [On local changes of tide heights and on the char- 

acter of the tide-wave.] Min. Proc. Inst. Civ. Eng. VII, 364, 1848. 

155. Wheeler, W. H. The Sea Coast; Destruction: Littoral Drift: Pro- 

tection, p. 8, London, 1902. 

156. Haupt, L. M. Discussion on the Dynamic Action of the Ocean in 

Building Bars. Proc. Am. Phil. Soc. XXVI, pp. 147, 148, 155, 1889. 

157. Marsh, Geo. P. The Earth as Modified by Human Action, p. 538, 

New York, 1907. 

158. Krummel, Otto. Handbuch der Ozeanographie. II. Die Bewegungs- 

formen des Meeres, p. 158, Stuttgart, 1911. 

159. Ibid., p. 166. 

160. Harris, R. A. Manual of Tides, Part V. U. S. Coast Surv. Rept. for 

1907. Appendix No. 6, 472-482, 1907. 



54 WATER WAVES 

161. Thoulet, J. Oceanographie Dynamique, pp. 71-84, Paris, 1896. 

162. Dawson, W. Bell. Illustrations of Remarkable Secondary Tidal 

Undulations in January, 1899, as Registered on Recording Tide 
Gauges in the Region of Nova Scotia. Trans. Roy. Soc. Canada. 
2nd Ser., V. Sec. Ill, 24, 1899. 

163. Darwin, G. R. The Tides and Kindred Phenomena in the Solar 

System, pp. 16-49, London, 1898. 

164. Sandstrom, J. W. Dynamische Versuche mit Meerwasser. Annalen 

der Hydrographie und Maritimen Meteorologie. XXXVI, 10, 1908. 

165. Helland-Hansen, Bjorn and Nansen, Fridtjof. The Norwegian 

Sea, p. 116, Christiania, 1909. 

166. Ekman, V. W. On Dead Water. The Norwegian North Polar Expedi- 

tion 1893-1896, Scientific Results. V, No. 15, p. 42, Christiania, 1906. 

167. Helland-Hansen, Bjorn and Nansen, Fridtjof. The Norwegian 

Sea, pp. 114-117, Christiania, 1909. 

168. Stokes, George Gabriel. On the Theory of Oscillatory Waves. 

Mathematical and Physical Papers, I, 212-219, 1880. 



CHAPTER II 
THE WORK OF WAVES 

Advance Summary. — Water waves, whose general charac- 
teristics were discussed in Chapter I, possess energy capable of 
effecting profound changes upon the margins of the land or 
upon artificial structures with which they may come into con- 
tact. Geologist, geographer, and engineer must each concern 
himself with the nature and magnitude k of wave energy, and 
with the manner in which waves accomplish their work. The 
layman finds the destructive energy of waves a source of inter- 
est and wonder, and not unnaturally regards the meeting-place 
of land and sea as one of the most fascinating of Nature's lab- 
oratories. 

In the present chapter the nature of wave energy is first dis- 
cussed, and the manner of wave attack upon cliffs and sloping 
shores is briefly treated. It is then shown that the dynamic 
pressures exerted by waves may be measured with reasonable 
exactness, and calculated and measured pressures are shown 
to be in substantial agreement. Some of the most striking 
examples of damage done by storm waves are next passed in 
review, in order that the reader may visualize the magnitude of 
the force responsible for the modification of shore features and 
the manifold methods of its working. In order to determine 
which parts of a shore or what artificial structures will suffer 
most from wave attack, it is essential to know precisely what 
factors control wave energy, and these are briefly considered. 
A process of "wave refraction " is shown to be responsible for 
the concentration of wave attack upon projecting headlands 
and for the comparative immunity of shores about the heads 
of bays. In conclusion, attention is directed to the vitally im- 
portant question as to how far below the water surface wave 
action may be appreciable. 

Wave Energy. — It can readily be shown that a wave transmits 
energy along the surface of a water body, and delivers this energy 
on the beach or against some artificial obstacle. When a ship is 

55 



56 THE WORK OF WAVES 

propelled through the water, a wave is pushed up by the bow. 
It took a certain amount of energy to raise this mound of water, 
and that amount was taken away from the energy of the moving 
vessel, thereby causing the vessel's motion to be retarded. The 
wave passes over the surface of the water; and if it finally dashes 
upon some beach, the energy there expended is the same energy 
imparted by the moving boat, less a small amount lost through 
friction. 

The mere spreading apart of the water by a vessel's bow does 
not require the expenditure of energy. If it were not for other 
causes of resistance, a ship once started through the water would 
move on forever, unimpeded by the pushing apart of the water 
in front. The common idea that a vessel's bow is made sharp 
so that it may cut into the water like a wedge and more easily 
push it out of the way, is erroneous. No part of the resistance 
to a ship's motion arises directly from the pushing of water to 
either side by the bow 1 . A great deal of resistance does arise, 
however, from the fact that energy is used up in making waves, 
and one object of the naval architect is to design a vessel of such 
form that it will produce the fewest and smallest waves possible. 

The energy of a wave depends upon its length and height, 
and is of two types : the kinetic energy due to the orbital move- 
ment of the water particles; and the potential energy due to the 
fact that the center of gravity of the mass of water composing 
a wave is raised slightly above the position it occupies when the 
water is at rest. It can be shown that the two types of energy 
are exactly equal in amount; in other words, the energy of a 
wave is half kinetic and half potential. Since we know that a 
cubic foot of sea water weighs about 64 pounds, it is easy to 
calculate the total energy of either shallow-water or deep-water 
waves in foot-tons per linear foot of wave crest. The formulae 
employed in such calculations are too complex for discussion 
here, but may be found in Gaillard's treatise 2 , and similar works. 

During the advance of a deep-water oscillatory wave one-half 
of the total wave energy is transmitted forward with the wave 
form. The energy of shallow-water oscillatory waves is from 1 
per cent to 11 per cent less than the energy of deep-water waves 
of equal length and height, but just as in the case of deep-water 
waves one-half the total wave energy is transmitted onward. 
In both cases it is the potential energy which is thus carried 



NATURE OF WAVE ATTACK 57 

forward with the wave 3 . In the wave of translation the energy 
is also partly kinetic and partly potential; but as this wave leaves 
still water behind it, at the original level, the entire wave energy 
must pass forward with the wave form. We have already seen 
that when oscillatory waves pass into water which shoals very 
gradually, they are slowly transformed into waves of translation, 
or at least acquire some of the characteristics of such waves. 
From this it follows that an oscillatory wave may, by changing 
into a wave of translation, deliver at the shore all, or nearly all, 
its energy 4 . This may help to explain the fact that the blows 
of storm waves against a cliff or sea wall often exceed in vio- 
lence the available energy calculated for the waves on the as- 
sumption that they are waves of oscillation. 

Nature of Wave Attack. — The nature of the force exerted by 
a wave upon any obstacle, such as a cliff or beach, depends in 
part upon the type of wave and its condition at the moment of 
collision with the obstacle. If an unbroken oscillatory wave 
strikes a vertical wall or cliff the base of which reaches down to 
deep water, the wave is reflected back. At the instant of con- 
tact the crest of the wave rises to twice its normal height and 
the cliff is subjected to the hydrostatic pressure of this unusually 
high water column. The absence of any forward thrust of the 
water mass under these conditions is shown by the behavior of 
boats which have been observed to rise and fall with successive 
waves without touching the vertical wall only a few feet distant. 
Hagen 5 concludes that under such circumstances debris must 
accumulate at the base of the wall and that therefore the preju- 
dice against vertical sea walls and harbor walls, based on the fear 
of undermining by wave action, is ill-founded. 

A wave of translation striking a vertical wall or cliff under the 
same circumstances is also reflected; but it delivers against the 
cliff a vigorous push due to the forward thrust of the whole mass 
of the wave, in addition to subjecting the obstruction to hydro- 
static pressure. Stevenson 6 found that " oscillatory waves become 
waves of translation when they reach the unfinished part of a ver- 
tical sea wall, and that they then exert a force nearly 6 times 
greater than if they had remained waves of oscillation." If either 
type of wave breaks just before reaching the cliff, in such manner 
that the forward falling crest of the wave strikes the cliff face, the 
only force exerted is that due to the forward motion of the water 



58 THE WORK OF WAVES 

particles. This motion may exceed the velocity of the wave 
itself at the time of breaking, the crest shooting forward beyond 
the main body of the wave as it falls. When an oscillatory 
wave breaks a short distance out in front of the cliff, so that 
the forward pitching crest does not strike the cliff, but plunges 
into the water at its base, the regular orbital motion is destroyed 
and a " whirlpool turbulence " is produced, the forces of which 
are not easily analyzed. In a similar manner, if a wave of 
translation breaks just before reaching a cliff, it " becomes a 
surge or broken foam, a disintegrated heap of water particles, 
having lost all continuity." The moving waters of the surge or 
whirlpool turbulence may exert considerable dynamic pressure 
on the base of the cliff, and some hydrostatic pressure, depend- 
ing on the height to which the water rises. When either oscil- 
latory waves or waves of translation break far out from the base 
of the cliff, smaller waves of translation may traverse the inter- 
vening water and operate upon the cliff in the manner already 
described. 

On a sloping shore of fairly steep inclination, oscillatory waves 
may arrive almost at the beach before losing their essential 
characters. When such a wave breaks the falling crest dashes 
down upon the water which is returning seaward from the swash 
of the preceding wave. The falling wave crest thus strikes a 
cushion of moving water which may be of considerable thickness. 
A zone of great confusion is thus produced, the force of the wave 
is largely dissipated, and part of its volume augments the sheet 
of water moving seaward, while a larger part starts up the beach. 
Almost instantly the remainder of the breaking wave over- 
takes the zone of disturbance, the forward oscillation under the 
crest checking and possibly reversing the seaward motion of 
the bottom water, while the landward moving water is enor- 
mously augmented in volume. At the same time the orbital 
motion of the water is largely destroyed, and in the form of a 
confused mass it rushes up the beach until stopped by gravity 
and friction, when it flows back with gradually increasing velocity 
to meet the next oncoming wave. Under these conditions much 
of the energy of the wave is consumed by friction in the turbulent 
waters, while another part is expended in the impact of the 
falling crest upon the bottom wherever the sheet of seaward 
moving water is effectively pierced. The beach itself is affected 



NATURE OF WAVE ATTACK 



59 




60 THE WORK OF WAVES 

mainly by the sheet of water which is propelled up the slope 
by the remnant of the wave's energy of motion, and which re- 
turns under the action of gravity. 

- It should be noted that after the oscillatory wave breaks, the 
confused mass of water propelled up the slope of the beach may 
be regarded as an irregular type of wave of translation. When 
a typical wave of translation breaks immediately at the foot of 
the beach, its falling crest must also meet the backward flowing 
water cast up by the preceding wave, and give rise to much the 
same phenomena as the breaking oscillatory wave. 

On a coast bordered by water so shallow that large oscillatory 
waves are broken some distance out from the shoreline, waves 
of translation and small oscillatory waves alone may reach the 
beach. If the beach slopes very gradually under water, there 
may be a secondary line of surf a short distance out where these 
waves break, and the amount of wave energy which finally 
reaches the beach itself may be quite insignificant. On the 
other hand, if the water between the shoreline and the zone 
where the great oscillatory waves break is of fairly constant 
depth, and the shore rises fairly abruptly at the inner margin 
of the shallow, waves of translation of considerable size may 
deliver their whole energy upon the beach. The latter is then 
subjected to the static pressure due to the wave height, and the 
dynamic force of the rapidly moving water particles. 

When a wave comes in contact with a vertical or very steep wall 
or cliff, a relatively small portion of the wave mass may be shot 
upward (Plates IV and V). It appears that under these circum- 
stances the energy of a large portion of the wave is suddenly 
communicated to the smaller water mass. The result is that the 
velocity of this mass may be very great, and it may deliver a blow 
of terrific force upon a small area. Overhanging cliffs or projec- 
tions from cliff faces, the roofs of sea caves, and other masses 
of rocks favorably situated may be subjected to blows from 
below which have the strength of a battering ram. The energy 
expended is the kinetic energy due to the swift motion of the 
water masses. 

Masses of water shot into the air in the manner just described 
may encounter no obstacle in their upward flight, but may 
descend upon the level summit or sloping face of a cliff, the sur- 
face of a beach, or some artificial structure. Such falling masses 



NATURE OF WAVE ATTACK 



61 



Plate V 




Photo by A. M. Crornack. 

Water forced vertically upward by wave breaking against sea wall at 
Scarborough, England. 



62 



THE WORK OF WAVES 



of water are capable of executing considerable damage because 
of the great energy they acquire by descending with the ever- 
increasing velocity due to gravitation. 

Wave Dynamometer. — Stevenson has shown that the action 
of a wave is not at all like the sudden impact of a hard body, but 
is analogous to the steady pressure of a current, because the wave 
acts with a continuous pressure for an appreciable length of 
time 7 . It follows from this that if waves are allowed to come 
against a vertical plate which has a spring back of it, and if the 




12 Inches 



Fig. 11. — Stevenson's Wave Dynamometer. 
DEFD is a cast-iron cylinder, bolted to the rock by the flanges at G. 



AA is 



an iron disk against which the waves impinge, fastened to guide rods BB, 
which pass through holes in the plate CC. When waves strike the disk 
AA, rings of leather TT are moved along the guide rods, registering the 
extent to which the spring is lengthened. LL is a door opened for the 
purpose of reading the instrument. 

change in length of the spring due to the pressure against the plate 
is determined, we shall have a proper measure of the dynamic 
pressure exerted by the wave. Stevenson 8 devised such an instru- 
ment, called a dynamometer, and was the first man to measure 
the force of waves. Gaillard confirmed Stevenson's results, but 
pointed out that the spring dynamometer measures only the dy- 
namic pressure of the moving water in the wave, and gives no 
information as to the static pressure resulting from the weight 
of the water mass. This is due to the fact that static pressure is 
just as great on the back of the plate as on the front, and therefore 
produces no effect on the spring. He therefore designed a dia- 



MEASUREMENTS OF WAVE ENERGY 63 

phragm dynamometer having a sheet of rubber stretched over 
one end of a short iron cylinder, the other end being closed by 
an iron plate. Pressures due to the waves thus affect but one 
side of the instrument by pushing in the rubber diaphragm, and 
the magnitudes of the pressures are determined by means of 
a gauge attached to the cylinder. To measure the static pres- 
sure due to the column of water in the wave the instrument .is 
placed with its face horizontal and upward at the desired depth 
in the water. When placed with its face vertical so as to receive 
the full impact of the advancing wave the instrument records 
both dynamic and static pressures 9 . 

Measurements of wave force with dynamometers indicate that 
the static pressures exerted by waves are considerably less than 
their dynamic pressures. On Lake Superior, Gaillard found the 
static pressure of a wave 10.5 feet high and 150 feet long, to be 
3.23 lbs. per square inch, or about 450 lbs. per square foot, the 
dynamometer being 9 feet below the wave crest. The dy- 
namic pressures of waves 10 feet high and 150 feet long varied 
from 460 to 965 lbs. per square foot on a dynamometer placed 
about a foot higher than that for the measurement of static 
pressures 10 . Adequate observations of wave pressures by means 
of suitable dynamometers have not yet been made, those for 
static pressures being especially insufficient in number. 

Measurements of Wave Energy. — In order to gain some con- 
ception of the enormous power of waves we have only to consider 
the theoretical pressures calculated for waves of different size, the 
actual pressures recorded by dynamometers on exposed coasts, or 
the damage to harbor works done by storm waves. Gaillard has 
calculated that a wave 10 feet high and 100 feet in length may 
strike an obstruction with a pressure of 1675 lbs. per square foot, 
while a wave 12 feet high and 200 feet long should exert a maximum 
dynamometer pressure of 2436 lbs. per square foot. The total 
theoretical energy of such a wave is 109 foot-tons for every 
linear foot of wave crest. Great ocean waves such as those 
which destroyed part of the breakwater at Wick, Scotland, in 
1872, if we assume a height of 42 feet and a length of 500 feet, 
should produce a pressure of 6340 pounds per square foot 11 . 

Dynamometer readings show that during storms on Lake 
Superior the waves develop a force of from 1600 to 2500 lbs. 
per square foot 12 . Stevenson found that the Atlantic Ocean 



64 



THE WORK OF WAVES 




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DAMAGE BY STORM WAVES 65 

waves near the island of Tyree on the Scottish coast had an 
average force of 611 lbs. per square foot during the summer 
months, whereas the average for the winter months was 2086 
lbs., or more than three times as great. The greatest force 
recorded at this point was 6083 lbs. or practically that calculated 
theoretically for a very large ocean wave. Another reading of 
5323 lbs. was secured. On the east coast of Scotland pressures 
of more than 6000 lbs. per square foot were recorded 13 . 

Damage by Storm Waves. — Such enormous pressures are cap- 
able of producing remarkable results. Stevenson describes an in- 
stance in which a block of stone weighing 1\ tons and situated 20 
feet above sealevel was driven before the waves for a distance of 
73 feet over rugged ledges 14 . At North Beach, Florida, a solid block 
of concrete weighing 4500 lbs. was moved 12 feet horizontally and 
turned over on its side, while a second block weighing 3600 lbs. and 
having its center at high-water level was shifted several inches 
by waves which were not over 4 feet high. During a severe 
storm on December 25, 1836, stones forming part of the break- 
waterat Cherbourg and weighing nearly 7000 lbs. were thrown 
over a wall 20 feet high which surmounts the stone embank- 
ment. In the harbor of Cette a block of concrete 2500 cubic 
feet in volume and weighing about 125 tons was shifted more 
than 3 feet from its original position. Perhaps the most won- 
derful example of wave work is that accomplished by ocean 
storm waves upon the breakwater at Wick in December, 1872, 
and described in Stevenson's treatise on " Harbors." The 
seaward end of this breakwater was protected by a monolithic 
block of cement rubble 45 feet long, 26 feet wide and 11 feet thick, 
and weighing more than 800 tons, resting on great blocks of 
stone which were bound solidly to the monolith by iron rods 3| 
inches in diameter running through holes in the stones and 
embedded in the cement rubble. The entire mass, weighing 
1350 tons, was torn from its place by the waves and dropped 
inside the pier, where it was found unbroken after the storm 
subsided. A much larger mass of concrete was substituted for 
the one removed, the new block having a volume of 1500 cubic 
yards, and weighing 2600 tons. In 1877 this enormous mass was 
similarly carried away by the waves 15 . 

The terrific impact which a wave may deliver against the 
face of a vertical wall may be appreciated from the fact that the 



66 THE WORK OF WAVES 

facing stones of the Wick breakwater, having the same density 
as granite, were shattered by the sea in February, 1872. At 
Dunkirk waves from the narrow southern arm of the North Sea 
strike the coast with an impact which causes a trembling of the 
ground more than a mile inland 16 . That waves have the power 
to wrench from place objects situated well above the main body 
of the wave is shown by the effects of a storm upon Dhuheartach 
lighthouse on the west coast of Scotland, during which fourteen 
stones weighing 2 tons each were torn from their positions 37 feet 
above high tide, and dropped into deep water. Cast-iron lamp 
posts on the pier heads at Duluth, located 19 feet above lake 
level, have repeatedly been broken off by wave action. 

The lifting power of waves is often illustrated by damage to har- 
bor works. At North Beach, Florida, a block of concrete weighing 
10J tons was lifted vertically upward three inches by the wave 
pressure transmitted through crevices below the mass. During 
a storm on Lake Superior a mass of trap rock 2 cubic yards in 
volume and weighing about \\ tons was raised by a wave from 
its place alongside an old breakwater at Duluth and deposited 
on the surface of the breakwater some 5 or 6 feet above its original 
position. A more striking example occurred at Ymuiden on the 
coast of Holland, when a concrete block weighing 20 tons was 
lifted 12 feet vertically by a wave and deposited on a pier above 
high-water level. 

Waves deflected upward by a sloping surface may accom- 
plish work at high levels. The keeper of Trinidad Head light 
station, on the Pacific Coast, reports that during the storm 
of December 28, 1913, the waves repeatedly washed over Pilot 
Rock, 103 feet high. One unusually large wave struck the 
cliffs below the light and rose as a solid sea apparently to the 
same level at which he was standing in the lantern, 196 feet 
above mean high water, the spray rising 25 feet or more higher. 
The shock of the impact against the cliffs and tower was terrific, 
and stopped the revolving of the light. Lake Superior waves 
reached the door of a light-keeper's dwelling situated 140 feet 
back from the water and 60§ feet above it, carrying away a 
board walk and doing other minor damage. On the Bound 
Skerry in the Shetland Islands blocks of stone from 6 to 13 tons 
in weight have been forced from their places at a level which is 
70 to 75 feet above the sea. 



DAMAGE BY STORM WAVES 67 

The destructive power of the masses of water hurled to re- 
markable heights by breaking waves is greater than one might 
suppose. At the Bell Rock lighthouse in the North Sea a ground- 
swell, without the aid of wind, drove water to the summit of the 
tower 106 feet above high tide, and broke off a ladder at an 
elevation of 86 feet. A bell weighing 3 cwt. was broken from 
its place in the Bishop Rock lighthouse, 100 feet above high 
water mark, during a gale in 1860; and at Unst, in the Shetland 
Islands, a door was broken open at a height of 195 feet above 
the sea. The keeper of Tillamook Rock lighthouse, on the coast 
of Oregon, reports that in the winter of 1902 the water of waves 
was thrown more than 200 feet above the level of the sea, de- 
scending upon the roof of his house in apparently solid 
masses. In October 1912, and again in November 1913, the 
panes of plate glass in the lantern of this same light, 132 feet 
above mean high water, were broken in by storm waves. 

Great damage may be accomplished by the falling water. Ac- 
cording to Shield 17 "it is no uncommon occurrence for storm waves, 
striking a vertical breakwater face, to throw heavy masses of 
water to a height of at least 100 feet, often very much higher. 
Such water in its descent on reaching the roadway of the break- 
water upon which it falls, will have attained a velocity of about 
80 feet per second, or nearly double the velocity and four times 
the force of the water striking the face of the breakwater." Dur- 
ing a severe gale at Buffalo in December, 1899, seventy big tim- 
bers, 12 X 12 inches in thickness, 12 feet long, and 10 feet between 
supports, were broken in two in the middle by the impact of the 
falling water. This same breakwater was further damaged a 
year later when waves breaking against it were hurled from 75 
to 125 feet into the air, the falling water crushing the big timbers 
on which it fell as though they had been pipestems. 

A part of the geological work accomplished by waves is due 
to the direct pressure exerted upon air and water imprisoned in 
crevices, and another part to the sudden expansion of air in 
crevices and pore spaces when the rapid retreat of a wave creates 
a partial vacuum outside. The effect of compressed air may be 
inferred from the fact that waves coming against a breakwater in 
Buffalo harbor produced such high pressure upon the air under the 
concrete shell that four circular plates of concrete, 3 feet in diam- 
eter, 6 inches thick and weighing 530 lbs. each, serving as covers to 



68 THE WORK OF WAVES 

manholes, were lifted from their places. A block weighing 7 tons 
in the face of the breakwater at Ymuiden was started forward out of 
its place during a gale, the movement being toward the waves which 
were coming against it. According to Gaillard this phenomenon 
was caused " by the stroke of a wave compressing the air in the 
rear of it" 18 , but similar results are produced by expansion due to 
the formation of a partial vacuum in front. In 1840 a securely 
fastened door in the Eddystone lighthouse was burst outward 
during the attack of storm waves, the circumstances leading 
Geikie to conclude that " by the sudden sinking of a mass of 
water hurled against the building, a partial vacuum was formed, 
and the air inside forced out the door in its efforts to restore the 
equilibrium' 119 . 

Another important factor in the work of waves is the effect pro- 
duced by stones, logs, blocks of ice, and other objects moving 
with the waves. It has been well said by Playfair 20 that waves 
thus armed become a sort of " powerful artillery " with which 
the ocean assails the land. A large block of ice or a log may 
concentrate its whole momentum upon a very small area with 
appropriately great results. Thus, Gaillard has suggested that 
an exceptionally high dynamometer reading on Lake Michigan 
(when the instrument showed a pressure twice as great as that 
recorded in the same locality for a more severe storm and greater 
than any record for the larger waves of Lake Superior) may 
possibly have been caused by ice or timber. Large stones may 
be hurled out of the water with high velocities. At Tilla- 
mook Rock on the Oregon Coast, fragments of stones are torn 
from the cliffs during every severe storm and thrown on the 
roof of the light-keeper's house, about 100 feet above sealevel. 
" In December, 1894, one fragment weighing 135 lbs. was thrown 
clear above this building, and in falling broke a hole 20 feet 
square through the roof, practically wrecking the interior of the 
building. Thirteen panes of glass in the lantern were broken 
during the same storm" 21 . As already noted, this lantern is 
132 feet above mean high water. The fog-signal siren horns, 
about 95 feet above the sea, were partially filled with rocks during 
the storm of October 18, 1912. The windows of the Dunnet 
Head lighthouse on the north coast of Scotland, which are over 
300 feet above high-water mark, are sometimes broken by stones 
swept up the cliffs by waves 22 . 



DAMAGE BY STORM WAVES 69 

It is perfectly evident that waves which are armed with 
cobblestones and enormous boulders must accomplish great 
erosive work when they beat against a cliff or artificial wall. On 
the other hand, one must not make the mistake of assuming 
that waves which are not thus armed can accomplish but little 
work. It is true that large storm waves may beat against a 
cliff without removing the barnacles which are attached to its 
face, and that along the shores of saline lakes calcareous tufa 
may form on cliffs exposed to the impact of large waves 23 . But 
this merely indicates that the pressure of the liquid mass is so 
evenly distributed upon all sides of the strong shell, or of the 
mineral deposit, that the excess of pressure on any one side is 
not sufficiently great nor applied with sufficient suddenness to 
cause rupture. The same waves will wrench great blocks of 
rock from their places in the cliff face, and drive air and water 
into joint crevices with such force as to loosen large fragments 
of the cliff and thus contribute to the disintegration of the whole 
mass. A force which exerts a pressure of thousands of pounds 
to the square foot will discover lines of weakness in any natural 
cliff. Even though all sand, boulders, and other rock fragments 
were speedily carried out of the zone of wave action, and waves 
of pure water alone attacked the coasts, shorelines would retreat 
under wave erosion just as surely as they do when the waves 
are armed with abrasive materials, although the process would 
certainly go on much more slowly. 

British geologists have long appreciated the tremendous power 
of the waves in destroying land areas, and with good cause; for 
no part of the British Isles is far removed from the sea, the wave 
attack on much of the coast is remarkably vigorous, and abundant 
ancient records and surveys permit careful computation of the 
rate of cliff retreat at many points. Old maps of Yorkshire show 
the location of many towns and villages which have been swept 
out of existence by the waves, their former sites being now re- 
presented by sandbanks far out in the sea. In 1829 there was 
in the harbor of Sheringham, according to Lyell 24 , a depth of 20 
feet of water where only forty-eight years before had stood a 
cliff fifty feet high with houses upon it. For over half a century 
the cliff at Happisburgh retreated at the rate of 7 feet per year, 
while the cliff between Cromer and Mundesley was cut back 
330 feet in the twenty-three years previous to 1861 making an 



~ 



70 



THE WORK OF WAVES 



s. 




DAMAGE BY STORM WAVES 71 

annual retreat of 14 feet. Matthews 25 estimates that the rate 
of cliff erosion on the Holderness coast of Yorkshire varies from 
7 feet per year in some places to 15 feet in others, while the 
retreat between Cromer and Mundesley since 1861 is said to 
have been 19 feet annually. At South wold the annual rate has 
varied from 15 to 45 feet. Shakespeare's cliff (Plate VII) near 
Dover is so vigorously undermined that great landslides descend 
from the upper part of the cliff, the debris projecting far into the 
sea until the waves remove it and renew their attack on the 
cliff base. Such a landslide in 1810 caused a marked earth- 
quake at Dover. Detailed accounts of the rates of cliff erosion 
about the British Isles will be found in Lyell's " Principles of 
Geology " 26 , while Matthew's " Coast Erosion and Protection " 27 
gives more recent data on this question. Further details are 
abundantly set forth in the reports of the Royal Commission on 
Coast Erosion of Great Britain 28 . 

The large blocks of rock dislodged from cliff faces, as well as 
smaller fragments, are churned together by the waves so long 
as they remain within reach, either upon the beach slope or in 
shallow water. The surf zone has been likened by Shaler 29 to 
a great mill in which angular fragments are quickly rounded and 
everything in course of time is reduced to the size of sand or 
fine silt and swept out to sea. How effective is this mill may 
be inferred from the fact that angular fragments of granite from 
quarries on Cape Ann, Massachusetts, become fairly well rounded 
by wave action in a single year, while under favorable circum- 
stances " the wear upon the pebbles amounts on the average to 
several inches per annum " 30 . On a stormy day the roar of 
grinding masses of boulders often rises above the sullen thunder- 
ing of the surf. 

A vivid picture of the working of the " sea mill," which grinds 
great boulders to sand and fine mud, is given by Henwood 31 in an 
account of the visit made by him to a mine in southwest England 
which extended out under the sea: " When standing beneath 
the base of the cliff, and in that part of the mine where but nine 
feet of rock stood between us and the ocean, the heavy roll of 
the larger boulders, the ceaseless grinding of the pebbles, the 
fierce thundering of the billows, with the crackling and boiling 
as they rebounded, placed a tempest in its most appalling form 
too vividly before me to be ever forgotten. More than once 



72 ?HE WORK OF WAVES 

doubting the protection of. our rocky shield we retreated in 
affright; and it was only after repeated trials that we had con- 
fidence to pursue our investigations." 

Conditions Affecting Wave Energy. — We have already seen 
that the dimensions of waves vary with differences in depth of 
water, strength and duration of wind, and length of fetch of 
open water. It follows from this that the amount of wave energy 
delivered against a shore will vary with these same factors. A 
coast bordered by off-shore shallows escapes the most powerful 
wave attack, because large waves cannot traverse the shallow 
water. Other things being equal, that part of a shoreline facing 
the greatest stretch of open water will receive the largest amount 
of wave energy. But it must be remembered that the prevailing 
winds may come across a shorter stretch of open water, with 
the result that what appear to be the less exposed parts of a 
shore may really suffer the more vigorous attack. Account 
must also be taken of the fact that the prevailing wind may not 
be the dominant wind; for a few great storms from one direction 
may more than offset the effect of long-continued wave attack 
from the direction of the prevailing wind. It is, therefore, not 
always a simple matter to determine which parts of a shore will 
suffer most from the energy of waves. The observer must 
carefully consider the inclination of the off-shore slope; the 
depth of water both near the shore and farther out; the pres- 
ence or absence of shallows ; the directions of the greatest stretch 
of open water, of the prevailing winds and of the greatest storm 
winds; and a number of other factors which may enter into the 
case; and must skilfully weigh the relative importance of each 
factor in a given case before he can reach a safe conclusion. 

Among the factors affecting the energy with which waves 
attack a shore are two not previously mentioned. These are 
tidal currents and the angle at which the waves meet the shore- 
line. When a wave encounters an opposing tidal current, the 
velocity and length of the wave are decreased, the height is 
increased, and the wave may break much as it would on a shel- 
ving beach. A swiftly moving tidal current may thus be quite 
as effective as a shallow in causing large waves to break before 
reaching the shore. The south coast of Shetland is protected 
from the waves of a southwest storm so long as a rapid tidal 
current off the coast is running, no matter how rough may be the 



CONDITIONS AFFECTING WAVE ENERGY 



73 




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•73 o 



i*S 



"Sb.b 

<3 ^h 



13 



74 THE WORK OF WAVES 

outside sea; but as soon as the current ceases the surf breaks on 
the shore with great force 32 . On the other hand, if the current 
is located immediately at the shore, and especially if it flows in 
the direction of wave advance, the destructive power of the 
waves may be augmented. Stevenson is of the opinion that 
the violence of the surf at Whalsey and Wick in northern Scot- 
land is in part due to the action of strong tidal currents; and at 
certain other places the surf seems to be most destructive when 
the tidal currents are strongest 33 . 

The angle at which the waves meet the shoreline has an im- 
portant effect upon the energy of wave attack. Waves are most 
destructive when they come in at right angles to the shoreline, 
and a very slight amount of obliquity materially decreases their 
power. Those portions of the breakwater at Wick which are 
assailed by waves coming " dead-on " have suffered much greater 
damage than other portions where the waves arrive at a slightly 
oblique angle 34 . It is therefore evident that where the direction 
of greatest fetch of open water makes an oolique angle with the 
shoreline, waves from that direction may be less destructive than 
waves developed on a shorter stretch of open water but approach- 
ing the land at right angles to the shore. It must not be sup- 
posed, however, that waves approaching a coast from a given 
direction maintain that direction until they break upon the 
beach. On the contrary, there is a very marked tendency for 
every wave to change its direction in such manner as to make its 
crest parallel with, and its direction of advance at right angles 
to the shoreline. Inasmuch as this tendency has an important 
effect upon the development of shorelines, we must give it some 
further consideration. 

Wave Refraction. — When a wave (ad, Fig. 12) advances toward 
a coast, the direction of advance is always at right angles to the 
wave crest. Nearing the coast, the wave encounters shallower 
water off the headlands than opposite the bays; and since the 
velocity of shallow-water waves decreases with decreasing depth, 
those parts of a wave opposite headlands will lag behind the parts 
opposite bays, and the wave crest will begin to curve (a l d l ) in 
conformity with the curves of the shoreline. If the headlands 
and bays are not too pronounced, and if the shallowing of the 
water is not too abrupt, by the time the wave has reached the 
position a?d 3 it will have so adjusted itself as to bring its crest 



WAVE REFRACTION 



75 



at all points nearly parallel to the shoreline. Or, as Harrison 35 
has expressed it, " the velocity of the part which first reaches the 
shallow being lessened, the whole wave wheels round, and 
breaks nearly at right angles on the beach." This process of 
" wave refraction," as Davis has called it, accounts for the fact 
that swells from distant storms ordinarily are nearly parallel to 




id 



Fig. 12. — Diagram 'to illustrate the process of wave refraction, whereby 
wave attack is concentrated on headlands. (After Davis.) 

the shore when they break, no matter what may have been the 
direction of the storm. Even within the narrow limits of a single 
curved beach an observer may note the tendency of the surf to 
break directly on shore throughout its length, although the beach 
may describe an arc of 90 degrees or more. 

An important consequence of wave refraction is the concen- 
tration of wave energy upon headlands. Since the direction 



76 THE WORK OF WAVES 

of wave advance is always at right angles to the crestline, and 
the latter becomes curved to conform with the curvature of the 
shoreline, it follows that a large proportion of the waves will be 
refracted toward the headlands. In Fig. 12 it is apparent that all 
that portion of the wave between a and b will be concentrated 
upon the short stretch of shoreline, AB, on the headland; 
whereas the part of the wave between b and c will be distributed 
over the great stretch of the bay shore, BC. In other words, 
wave refraction causes an enormous concentration of wave energy 
upon headlands and a dissipation of energy in bays. The ob- 
server who wishes to witness the most sublime manifestations of 
the power of the sea must seek the exposed headlands of the 
coast; while the mariner finds comparative safety within the 
limits of the bays, even where these are broadly open to the sea. 

Waves do not always break parallel to the shore. In the 
first place, no wave can be refracted with sufficient abruptness 
to render its crest parallel to the sharp and complex irregularities 
of some shores. In the second place, the water is very deep 
close to some shores, and wave refraction does not begin to take 
place until the wave has practically reached the headlands. 
The wave then breaks against these projecting points of the 
coast first, and its remaining portions, being imperfectly re- 
fracted, sweep upon the shore from the headlands inward at an 
oblique angle. Furthermore " forced waves," or those which 
are still being driven forward by the wind which formed them, 
are not so readily refracted as " free waves " which have passed 
beyond the limits of the storm. It is for this reason that storm 
waves are more apt to strike the shore at an oblique angle than 
are the groundswells which arrive during calm weather. The 
more perfect refraction of the groundswells is due not alone to 
the absence of the wind's impelling force, but probably also 
to the fact that they extend to greater depths and hence are 
the sooner affected by the refracting influence of a shallowing 
bottom. 

Depth of Wave Action. — The depth to which the ocean waters 
are affected by waves is a matter of much importance to all 
students of shore processes. We have already seen that 
at the depth of one wave length below the surface the water 
particles of oscillatory waves are moving in orbits whose di- 
ameters are only z ^ 5 as great as the diameters of the orbits at 



DEPTH OF WAVE ACTION 77 

the surface. Since the period of the lower orbits is identical with 
that of the larger surface orbits, it follows that the velocity of 
the water particles decreases in the same proportion as the di- 
ameters of the orbits. In other words, the water particles at 
the depth of one wave length below the surface move with 5^5 
of the velocity of the surface particles. The ability of oscil- 
latory waves to erode the bottom and to transport debris there- 
fore diminishes rapidly with increasing depth, and soon becomes 
negligible. In the case of waves of translation the motion of the 
water particles is theoretically the same from the surface to the 
bottom, except that the velocity near the bottom should be 
somewhat less than near the surface, owing to the fact that 
the water particles there pass through shorter, more nearly hori- 
zontal paths in the same length of time. With these theo- 
retical points in mind it will be interesting to inquire into the 
results obtained by different students of this phase of wave 
activity, and to review their opinions as to the maximum depth 
of efficient wave action in nature. Unfortunately, few writers 
distinguish between the effects of oscillatory waves and waves 
of translation. 

Captain E. K. Calver, R. N., has observed waves which changed 
their color upon passing into water from 40 to 50 feet deep be- 
cause of their abrasive action upon the bottom 36 . Sir John 
Coode studied the movement of shingle in the vicinity of the 
Chesil Bank on the south coast of England, by descending to a 
depth of 60 or 65 feet below the surface of the sea in diving dress. 
He found that after a heavy storm the shingle, which was pre- 
viously covered with barnacles, was quite free from these shells, 
proving a movement of the coarse material at a depth of nearly 
50 feet 37 . According to Hermann Fol, whose " Impressions 
d'un Scaphan drier " are vividly recorded in the Revue Scienti- 
fique for 1890 38 , a diver at a depth of 100 feet is tossed back and 
forth by the vigorous oscillatory movement of the bottom water 
whenever groundswells are running on the surface. Hunt quotes 
the testimony of pilots and masters to the effect that after a 
wave has broken over a vessel, sand is frequently left on the 
decks even when the water has a depth of 75 or 80 feet 39 , and 
describes a jar brought up in a trawl from a depth of 220 feet 
into which gravel the size of a hazelnut had been washed by 
wave agitation. Robert Stevenson states that fish disappear 



^ 



78 



THE WORK OF WAVES 



X 




I 

K 
I 

of 



DEPTH OF WAVE ACTION 79 

from the fishing grounds in the North Sea during storms, due 
to the agitation of the water by wave action to a depth of 200 
feet or more 40 . The same authority notes that at the Bell Rock 
lighthouse, off the east coast of Scotland, large stones, contain- 
ing upwards of 30 cubic feet and weighing two tons or more, 
are often thrown upon the rock from " deep water " by the 
waves 41 . Thomas Stevenson has made a very interesting com- 
parison between the depths at which mud reposes on the floor 
of different parts of the North Sea, and the vigor of wave ac- 
tion in those places. He finds that there is a direct relation 
between these two phenomena, the depth of the level at which 
mud accumulates increasing in much the same proportion as the 
violence of the waves. From this we may infer that the upper 
limit of mud accumulation is a measure of the maximum depth 
of wave disturbance in a given locality. Applying this rule 
to the North Sea, we find that in protected areas, as the inner 
parts of the Moray Firth and the Firth of Forth, and along the 
Holland coast in the narrow southern part of the sea, wave 
action reaches to a depth of 25, 50, or 100 feet; while in exposed 
places the disturbance is appreciable to a depth of from 300 to 
500 feet or more 42 . According to J. N. Douglas, the fishermen 
off Land's End bring up stones one pound in weight, which have 
been washed into their lobster pots at a depth of 180 feet by the 
action of the ground-swell, while coarse sand is often washed 
from a depth of 150 feet by storm waves and hurled to the lan- 
tern gallery of the Bishop Rock lighthouse, 120 feet above low- 
water 43 . Kinahan reports the moving of stones weighing several 
hundred pounds by wave action in water from 90 to 120 feet 
deep on the coast of Galway 44 . 

In contrast to the above records of significant wave action 
at great depths, may be mentioned a few instances of the ineffi- 
ciency of wave action a short distance below the surface. At 
the Cherbourg breakwater blocks of rubble stone 23 to 26 feet 
below low-water are reported by Wheeler as remaining unmoved 
in the roughest sea. According to the same authority, the 
rubble mound upon which the Alderney breakwater was later 
erected remained three years undisturbed by winter storms below 
the level of 15 feet below low- water 45 . Indeed, Wheeler goes to 
the extreme of limiting " the disturbance caused by the for- 
mation of waves ... to a distance below the surface about 



80 THE WORK OF WAVES 

equal to the height of the wave" 46 . At Port Elizabeth, in South 
Africa, Mr. Shield found that blocks of rubble stone, weighing 
from 1 to l\ cwt. remained unmoved at a depth of 22 feet when 
the waves were 15 to 20 feet high 47 . Coode reports that in the 
same locality the movement of sand on the sea-bottom ceases 20 
feet below the surface 48 . Delesse states that submarine portions 
of engineering structures are seldom disturbed below a depth of 
16 feet in the Mediterranean, and 26 feet in the Atlantic 49 . 

Too much importance must not be attached to the negative 
results just mentioned. In some of the cases we are not in 
possession of sufficient information regarding the degree of ex- 
posure of the localities in question, or of the size of the waves 
there generated. Engineering structures and masses of rubble 
stones may be so keyed together, or may have such external 
forms, as to receive the shock of vigorous waves without harm, 
while loose materials on the bottom are at the same time ma- 
terially affected. High waves of short length will not affect the 
water to as great a depth as lower waves of greater length. The 
positive evidence of wave disturbance at depths of several hun- 
dred feet is sufficient to prove that however ineffective some 
waves may be, other waves under favorable conditions will pro- 
duce an effect in deep water. We may take 600 feet as the limit- 
ing depth of ordinary wave disturbance, although Cornish sets 
900 feet as the limit for the largest recorded waves 50 . Geikie 
states that ripple marks are sometimes produced (by waves) 
in fine sand at a depth of 600 feet, and Airy apparently attributes 
the breaking of groundswells in water of the same depth to 
interference with the bottom 51 . Agassiz seems to recognize 
the possibility of wave action off the coast of Florida to a depth 
of 600 feet 52 . More definite figures are given by Cialdi, who 
asserts that large waves will erode the bottom to a depth of 40 
meters in the English Channel and Adriatic Sea, 50 meters in 
the Mediterranean Sea, and 200 meters, or about 650 feet, 
in the open ocean; and that at such depths the waves will put 
debris in motion and grind it together 53 . Still more convincing 
are the results of experiments made by "Siau 54 near Saint-Gilles 
on the Isle of Bourbon, off the coast of Madagascar. This in- 
genious investigator found that by sounding with a weight well 
coated with tallow he could determine the presence of ripple 
marks on the sea-bottom not only because the impression of 



DEPTH OF WAVE ACTION 81 

the ripples was imprinted upon the tallow surface, but also be- 
cause the heavy particles concentrated in the troughs and the 
light particles collected on the crests of the ripples adhered to 
the tallow in parallel bands. In this way Siau was able to prove 
the existence of wave-formed ripple marks, and hence of wave 
action, at a depth of 617 feet. In a letter to Nansen 55 Sir John 
Murray states that great storms off the north coast of Scotland 
agitate fine mud at a depth of 600 feet. Murray also quotes 
Vionnois as authority for the statement that in the Bay of St. 
Jean de Luz the bottom is agitated during storms at a depth 
of 300 meters, or nearly 1000 feet 56 . Unfortunately, while these 
authors evidently refer to oscillatory waves in their discussions, 
they do not definitely exclude the possibility that waves of 
translation may be responsible for the deep-water movements. 
Nor can we be certain, in some of the cases cited, that currents 
may not have produced the ripple marks and other phenomena 
attributed to wave action. 

There is no theoretical reason, however, why we should doubt 
the possibility of appreciable oscillatory wave action down to a 
depth of 600 feet. Observations with the naked eye and with the 
microscope convinced the Weber brothers that during the passage 
of oscillatory waves there is some slight mov ment of the water 
particles to a depth below the surface equal to 350 times the 
height of the waves 57 . Accordingly a wave 40 eet high should 
affect water particles 14,000 feet below the surface. At a depth 
of but 600 feet this movement must be quite pronounced, de- 
spite the rapid decrease in amplitude of oscillation from the 
surface downward, and notwithstanding that the maximum 
theoretical depth of wave disturbance may not ordinarily be 
attained in the ocean because of the long time required for the 
downward transmission of surface oscillations, which latter may 
cease or change direction before the lowest water strata are set 
in motion 58 . Assuming a groundswell with a length of 1350 
feet and a height of 16 feet, which is well within the possible 
limits, the water particles at a depth of 600 feet (f of the wave 
length) would move in orbits having a diameter of 1 foot. The 
period of such a wave is about 16 seconds; hence the water 
particles at the depth indicated would oscillate with a maximum 
velocity of 1 foot in 5 seconds, or .06 meter per second. If at 
the bottom the path of oscillation were reduced to a straight 



82 THE WORK OF WAVES 

line 1 foot in length, the velocity for a wave of the same period 
would be about .04 meter per second. Such an oscillation would 
disturb clay, fine mud, and probably the very finest sands. 
Forbes has shown that fresh water moving in a shallow trough 
with a velocity of .077 meter per second will stir up moist brick 
clay 59 , while Sorby recently found that a current of 6 inches 
(.15 meters) per second would drift along common sand grains 
one hundredth of an inch in diameter and that " the very fine 
Alum-Bay sand ^tU mcn m diameter " would be moved by a 
velocity as low as .04 meter 60 . According to de Lapparent a 
river with a bottom velocity of .15 meter per second will trans- 
port coarse mud 61 , whereas Lyell says this same velocity will 
move fine sand, and Hunt puts the lower limit for ordinary 
fine sand at .10 meter per second. The foregoing figures are 
based on observations in shallow fresh water. If we consider 
the conditions of temperature, pressure, salinity and viscosity 
which would exist at a depth of 600 feet in the sea, we find that 
sand particles of a given diameter ought to be moved by a slightly 
lower current velocity than in the cases cited. It seems reason- 
ably certain, therefore, that with an orbital diameter of 1 foot 
and a period of 16 seconds there would be appreciable distur- 
bance of the finer deposits on the sea floor. Even were the or- 
bital diameters as small as 1 inch and the period from 10 to 20 
seconds, Cornish is of the opinion that the motion of the water 
would still be sufficient to hinder the deposition of the finest 
kinds of mud 62 . When associated with slow-moving tidal or 
other currents, a very gentle oscillatory movement of the water 
due to wave action may produce an important effect. 

In the words of Cornish, " We may say with confidence, as a 
theoretical inference, that the agitation of wind-formed waves 
affects the bottom of the sea as far as the edge of the continental 
platform to such an extent as (in co-operation with tidal and 
other currents) to keep very fine mud moving about until it 
has an opportunity of subsiding over the edge of the continental 
shelf " 63 . On the other hand, it is evident that only the finest 
material will be affected at such depths, and that erosion of the 
bottom will be almost imperceptibly slight, so long as oscillatory 
waves alone disturb the water. Waves of translation are not as 
common in such deep water as nearer shore, but whenever they 
do occur we should expect, on theoretical grounds, a velocity of 



REFERENCES 83 

the bottom water comparable to that at the surface, and there- 
fore capable of effecting noteworthy erosion and transportation. 
A sufficient body of observed facts to establish this theory is not 
available. We are reasonably sure, however, that on exposed 
coasts the sea-bottom is not wholly free from some kind of wave 
agitation down to a depth of 600 feet at least. 

RESUME 

We have inquired into the origin and character of the 
energy developed by waves, and have gained some idea of the 
tremendous power which they may exercise under favorable 
conditions. It has been seen that natural shores, as well as arti- 
ficial structures, must suffer severely from wave attack. The 
conditions affecting the vigor of wave action at the shore have 
briefly been discussed, and the effects of wave refraction con- 
sidered more fully. An inquiry as to the depth of wave action 
has resulted in the conclusion that the sea-bottom is affected by 
waves to the edge of the continental shelf, or approximately to 
a depth of 600 feet. 

But waves are not the only forces of nature which expend 
their energy upon shores. Currents of various types play an 
important r61e in modelling shore forms, and must therefore 
receive our attention before we proceed to a study of the evolution 
of shorelines under the combined influence of waves and currents. 



REFERENCES 

1. Ekman, V. W. On Dead Water. The Norwegian North Polar Expe- 

dition, 1893-1896, Scientific Results. V, No. 15, p. 33, Christiania, 
1906. 
Fleming, J. A. Waves and Ripples in Water, Air, and iEther, p. 68, 
London, 1902. 

2. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 

Corps of Engineers U. S. Army, Professional Paper No. 31, pp. 40, 
46, Washington, 1904. 

3. Ibid., pp. 40, 45, 47, 50. 

4. Ibid., p. 51. 

5. Hagen, G. Handbuch der Wasserbaukunst. 3. Teil. Das Meer. I. 

Band, p. 97, Berlin, 1863. 

6. Stevenson, Thomas. The Design and Construction of Harbours. 

3rd Edition, p. 98, Edinburgh, 1886. 

7. Ibid., pp. 61-62. 



84 THE WORK OF WAVES 

8. Stevenson, Thomas. Account of Experiments upon the Force of the 
Waves of the Atlantic and German Oceans. Trans. Roy. Soc.Edin. 
XVI, 23-32, 1849. 
[ 9. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 
Corps of Engineers U. S. Army, Professional Paper No. 31, pp. 
161-171, Washington, 1904. 

10. Ibid., pp. 164, 167. 

11. Ibid., pp. 194-211. 

12. Ibid., p. 206. 

13. Stevenson, Thomas. Account of Experiments upon the Force of the 

Waves of the Atlantic and German Oceans. Trans. Roy. Soc. Edin. 
"~ XVI, 25, 1849. 

Stevenson, Thomas. The Design and Construction of Harbours. 
3rd Edition, pp. 55-57, Edinburgh, 1886. 

14. Stevenson, Thoma . The Design and Construction of Harbours. 

3rd Edition, p. 47, Edinburgh, 1886. 

15. Ibid., pp. 49-52. 

16. Meunier, Stanislas. La Geologie Experimental, p. 86, Paris, 1899. 

17. Shield, William. Principles and Practice of Harbor Construction, 

p. 81, London, 1895. 

18. Gaillard, D. D. Wave Action in Relation to Engineering Structures, 

Corps of Engineers U. S. Army, Professional Paper No. 31, p. 126, 
Washington, 1904. 

19. Geike, A. Textbook of Geology. 4th Edition, I, 568, London, 1903. 

20. Playfair, John. Illustrations of the Huttonian Theory of the Earth, 

p. 101, Edinburgh, 1802. 

21. Gaillard, D. D. Wave Action in Relation to Engineering Structures, 

Corps of Engineers U. S. Army, Professional Paper No. 31, p. 128, 
Washington, 1904. 

22. Geikie, A. Textbook of Geology. 4th Edition, I, 561, 1903. 

23. Gilbert, G. K. The Topographic Features of Lake Shores. U. S. 

Geological Survey. 5th Ann. Report, p. 81, 1885. 

24. Lyell, Charles. Principles of Geology. 11th Edition, I, p. 517, 

New York, 1873. 

25. Matthews, E. R. Coast Erosion and Protection, p. 11, London. 

1913. 

26. Lyell, Charles. Principles of Geology. 11th Edition, I, 671 pp., New 

York, 1873. 

27. Matthews, E. R. Coast Erosion and Protection. 147 pp., London, 

1913. 

28. Royal Commission on Coast Erosion. Minutes of Evidence. Reports 

of the Commission. I, Part 2, 1-504, 1907. 

29. Shaler, N. S. Beaches and Tidal Marshes of the Atlantic Coast. 

National Geographic Monograph, I, 143, 1895. 

30. Shaler, N. S. The Geology of Cape Ann, Massachusetts. U. S. Geo- 

logical Survey, 9th Ann Report, p. 565, 1889. 

31. Henwood, W. J. On the Metalliferous Deposits of Cornwall and 

Devon. Trans. Geol. Soc. Cornwall. V, 11, 1843. 



REFERENCES 85 

32. Stevenson, Thomas. The Design and Construction of Harbours. 

3rd Edition, p. 64, Edinburgh, 1886. 

33. Ibid., pp. 70-72. 

34. Ibid., pp. 35-37, 72. 

35. Harrison, J. T. Observations on the Causes that are in Constant 

Operation Tending to Alter the Outline of the English Coast, to Affect 
the Entrances of the Rivers and Harbours, and to Form Shoals and 
Deeps in the Bed of the Sea. Min. Proc. Inst. Civ. Eng., VII, 343, 
1848. 

36. Stevenson, Thomas. The Design and Construction of Harbours. 

3rd Edition, p. 20, Edinburgh, 1886. 

37. Coode, John. Description of the Chesil Bank, with Remarks upon 

its Origin, the Causes which have Contributed to its Formation, and 
upon the Movement of Shingle generally. Min. Proc. Inst. Civ. 
Eng., XII, 534, 1853. 

38. Fol, Hermann. Les Impressions d'un Scaphandrier. Revue Scien- 

tifique, XLV, 715, 1890. 

39. Hunt, A. R. On the Formation of Ripplemark. Proc. Roy. Soc. 

London. XXXIV, pp. 9, 15, 1882. 

40. Stevenson, Robert. On the Bed of the German Ocean, or North 

Sea. Memoirs Wernerian Nat. Hist. Soc. Trans., Ill, 332, 1821. 

41. Ibid., p. 332. 

42. Stevenson, Thomas. The Design and Construction of Harbours. 3rd 

Edition, pp. 21-25, Edinburgh, 1886. 

43. Douglas, J. N. [On the depth of wave action.] Min. Proc. Inst. Civ. 

Engineers. XL, 103, 1875. 

44. Kinahan, G. H. The Travelling of Sea Beaches. Min. Proc. Inst. Civ. 

Eng., LVIII, 284, 1879. 

45. Wheeler, W. H. A Practical Manual of Tides and Waves, p. 119, 

London, 1906. 

46. Ibid., p. 118. 

47. Ibid., p. 119. 

48. Coode, John. [On the depth of wave action.] Min. Proc. Inst. Civ. 

Eng., LXX, 45, 1882. 

49. Delesse, M. Lithologie des Mers de France, p. 110, Paris, 1872. 

50. Cornish, Vaughan. On Sea Beaches and Sand Banks. Geog. Jour., 

XI, 531, London, 1898. 

51. Geikie, A. Textbook of Geology. 4th Edition, I, 562, London, 1903. 
Airy, G. B. On Tides and Waves. Encyclopedia Metropolitana. V, 

351, 1848. 

52. Agassiz, Alexander. The Tortugas and Florida Reefs. Memoirs Amer 

Acad. Arts and Sciences, XI, 108, 1888. 

53. Cialdi, Alessandro. Sul Moto Ondoso del Mare e su le Correnti di esso, 

p. 555, Rome, 1866. 

54. Siau. De F Action des Vagues a de Grandes Profondeurs. Comptes 

Rendus de l'Academie des Sciences. XII, 774-776, 1841. 

55. Nansen, Fridtjof. The Bathymetrical Features of the North Polar Seas. 

The Norwegian North Polar Expedition. IV, Art. XIII, p. 137, 1904. 



86 THE WORK OF WAVES 

56. Murray, John. [On movement of shingle in deep water.] In discus- 

sion of paper by John Coode, on Chesil Bank. Min. Proc. Inst. Civ. 
Eng., XII, 551, 1853. 

57. Weber, Ernst Heinrich and Wilhelm. Wellenlehre auf Experimente 

Gegrundet, p. 126, Leipzig, 1825. 

58. Thou let, J. Oceanographie Dynamique, p. 57, Paris, 1896. 

59. Forbes, Edward. Abrading Power of Water at Different Velocities. 

Proc. Roy. Soc. Edinburgh, III, 474, 1856. 

60. Sorby, H. C. On the Application of Quantitative Methods to the 

Study of the Structure and History of Rocks. Quart. Jour. Geol. 
Soc. London. LXIV, pp. 180-181, 1908. 

61. Lapparent, A. de. Traite de Geologie; Phenomenes Actuels, p. 183, 

Paris, 1900. 

62. Cornish, Vaughan. Waves of the Sea and Other Water Waves, p. 145, 

Chicago, 1911. 

63. Ibid., p. 145. , 



CHAPTER III 
CURRENT ACTION 

Advance Summary. — Shore debris is subject to transpor- 
tation by many different kinds of currents. It is the purpose 
of the present chapter to discuss the more important of these 
currents and to describe the movements of debris which they 
cause. Following a brief preliminary summary of the types of 
currents to be treated, there is presented a detailed analysis 
of wave currents, and of the profoundly important process of 
" beach drifting" for which they are responsible. Tidal cur- 
rents are next considered, and while their value as a factor in 
beach construction has undoubtedly been much exaggerated, 
it is shown that they perform a significant function in modi- 
fying shores, particularly the shores of estuaries. Currents gen- 
erated by seiches have but a theoretical importance, except in 
a very few localities, and therefore receive but scant attention 
here. Currents caused directly by the friction of winds blowing 
over water surfaces deserve a more extended treatment. It 
will be seen that such currents are in some cases of a perma- 
nent character, in others purely temporary, while a third group 
varies in direction or character with changes in the seasons. 
Some of these "wind currents " are far removed from the lands 
and consequently play no role in shore development; but 
others locally wash the margins of continents or islands and have 
their share in shoreline work. 

A special class of currents, generated by winds but modified 
by other causes, comprises the great whirls of the~major oceanic 
circulation, and these are treated separately under the name 
" planetary currents." They seldom come in direct contact 
with the lands and are therefore of minor importance to the 
student of shorelines. Currents due to differences in atmos- 
pheric pressure, and convection currents, are likewise shown to 
play but an insignificant role in shore processes. Salinity cur- 
rents, arising from differences in specific gravity between waters 
having a different salt content, are well developed in certain 

87 



88 CURRENT ACTION 

straits, where they may locally control the movements of debris. 
For this reason currents of this type are treated somewhat fully 
and special consideration is given to examples at the mouths of 
the Baltic, Mediterranean and Red seas. River currents and 
their relation to delta growth are briefly described, and a similar 
treatment is accorded the " reaction currents" which flow into 
river mouths under certain conditions. Neither type of current 
deserves a major place in our discussion. Eddy currents, fre- 
quently associated with some of the currents mentioned above, 
deserve and receive a short space in our text. The important 
hydraulic currents generated as by-products of various other 
types of currents are not treated separately, but in association 
with the movements with which they are genetically connected. 
The chapter closes with a special consideration of the great 
complexities of current action. 

Types of Currents. — If we define a current as a more or less 
restricted body of water moving in a definite direction, it is evi- 
dent that various types of currents may exist in the sea. During 
oscillatory wave motion, masses of water moye first forward, then 
backward; and in waves of translation there is a forward movement, 
then a halt, followed by another forward movement, and so on. 
These short but of repeated movements of the water may affect 
shore deposits in much the same manner as more continuous 
currents, and we may therefore speak of them as wave currents. 
They are in many respects analogous to those currents which are 
associated with the great oscillatory movement of the sea water 
known as the tide, and which are commonly called tidal currents. 
Bays and straits, as well as lakes, have periodic oscillations of 
their waters called seiches. If these oscillations are of con- 
siderable amplitude, the rising and falling of the water give rise 
to seiche currents which in narrow straits may attain a fairly 
high velocity. It is well known that the wind tends to drag the 
surface layers of a water body along with it, thus producing 
within a very short time a distinctly noticeable wind current, or 
" wind drift " as it is more often called. The great systems of 
prevailing winds combined with the modifying effects of the 
earth's rotation, the forms of land masses, and other factors, have 
generated permanent systems of currents in the principal oceans. 
These are developed on a gigantic scale and are commonly dis- 
tinguished from the local currents produced by wind action alone. 



TYPES OF CURRENTS 89 

Since currents of this type must be characteristic of "any ro- 
tating planet which possesses an atmosphere and oceans, we may 
refer to them as planetary currents. Barometric pressures being 
greater in one place t-han in another, water may, under favorable 
conditions, flow from the region of high pressure toward that of 
low, as more or less distinct pressure currents. If one portion 
of the ocean is more highly heated than another, the difference 
in density between the lighter warm waters and the heavier cold 
waters will give rise to convection currents by means of which the 
waters will endeavor to re-establish a condition of equilibrium. 
In much the same manner oceanic waters, which are more saline 
and therefore heavier than adjacent waters, will produce ex- 
change currents with the lighter, less saline waters. We may 
for convenience call movements of this origin salinity currents. 
When rivers enter the sea their currents are progressively checked 
as they proceed farther and farther into the quieter water; but 
for some distance out from shore there may often be recognized 
very distinct river currents. The dynamic force of these out- 
flowing streams causes bottom currents which move landward 
into the river mouths, and which have been called reaction cur- 
rents. A current of any origin may be accompanied by lateral 
whirls or eddies, and these may be of sufficient diameter to give 
eddy currents of considerable importance. Whenever any one of 
the above types of currents impinges upon a coast, there results 
a piling up of the water with the consequent establishment of an 
hydraulic gradient. Water will flow from the higher to the lower 
level, and the resulting currents will here be spoken of as hy- 
draulic currents (" polarization currents " of Cornish 1 ) . A valuable 
discussion of the theory of some of the above mentioned types of 
currents will be found in a series of papers by V. W. Ekman 2 
published in the " Annalen der Hydrographie und Maritimen 
Meteorologie " in 1906. 

We will now consider the essential characters of the several 
types of currents in the order named above, except that it will 
be more convenient to treat the varieties of hydraulic currents in 
connection with the original currents which give rise to them. 
We shall purposely omit consideration of currents which are as 
yet but little known, such as the pulsating currents discovered 
off the Norwegian coast and described by Hellahd-Hansen 3 , 
and the deep vortices in the Norwegian sea described by Helland- 



90 CURRENT ACTION 

Hansen and Nansen 4 . We must not forget, however, that 
some of the movements thus omitted may ultimately prove of 
importance to the student of shoreline topography, for, in the 
language of the author last named, " the sea in motion is a far 
more complex thing than has hitherto been supposed," and, 
" there must be many forms of motion of great and far-reaching 
importance, though hitherto hardly known at all." 

Wave Currents. — It has already been shown that in normal 
oscillatory waves the water, from the surface downward, moves 
forward under the crest of each wave and backward under the 
trough. In shallow water this alternating current movement 
is accomplished without any accompanying vertical motion in 
that part of the water next to the bottom. The forward and 
the backward currents are approximately equal in duration, and 
on a level sea-bottom should nearly compensate each other. 
There will be a slight advantage in favor of the forward current, 
due to the slight progressive motion of the water particles in the 
direction of wave propagation which Stokes has shown to exist 
in oscillatory waves 5 . On shallow bottoms this would result 
in a slow advance of movable debris in the direction of wave 
propagation. 

Since the depth of wave action depends mainly upon the 
length of the waves, it is evident that the long groundswells 
which come from distant storms will affect the bottom waters 
more than will shorter storm waves developed near the coast. 
Storm waves may move landward or oceanward, according to 
the wind direction; but the swells always move landward. 
Hence the waves which most affect the bottom come on-shore; 
and the advantage resulting from the slight excess of the forward 
component of wave motion will be exerted mainly in a landward 
direction. On a level sea-bottom this would mean a transpor- 
tation of movable debris prevailingly in a landward direction. 

The advantage just referred to is often more than offset by 
the seaward slope of the bottom. If particles of debris are 
given a certain impulse up the incline, against the pull of gravity, 
they will travel a comparatively short distance ; if given a nearly 
equal impulse down the incline, in the direction of the pull of 
gravity, they will move a distinctly longer distance. Thus an 
alternating current with a slight excess of the shoreward com- 
ponent may cause a seaward transportation of debris on the 



WAVE CURRENTS 91 

ordinary offshore slope. Many authors, as for example Cor- 
naglia 6 , do not assign sufficient importance to the effects of 
gravity on a steep slope, the undertow, and other seaward-acting 
components to be discussed later; but consider that the normal 
consequence of wave action on the bottom is ordinarily to pro- 
duce a landward advance of debris of proper size and specific 
gravity. 

Where the water is so shallow in comparison with the wave 
length that there is produced a steepening of the wave front, 
another element is introduced. As Cornish 7 has pointed out, 
under these circumstances the forward motion is quick and short, 
the backward motion slower and of longer duration. This means 
that the shoreward component of such waves is much the more 
effective in moving coarser debris, since a shorter lived current 
of high velocity will transport material which is too large to be 
moved at all by the longer enduring but weaker seaward current. 
Sand and silt, on the contrary, will readily be moved a nearly 
equal distance in both directions, or on a sloping beach the sea- 
ward movement may predominate, as already shown. From this 
it follows that the same waves may drive pebbles and cobble- 
stones toward the beach and finer debris toward deep water, at 
one and the same moment. Or, as Cornish has well expressed it, 
" suitable oscillation on a seaward slope will set shingle travelling 
shoreward, and sand simultaneously travelling seaward " 8 . 

A further reason for the landward progress of coarse debris 
during wave action is elaborated by Cornish in his book on 
" Waves of the Sea and Other Water Waves " 9 . He shows that 
the forward current begins just as the vertical component of 
wave motion is raising coarse material from the bottom, with 
the result that this material is readily carried forward while in 
suspension; whereas the backward current sets in while the 
water particles are descending in their orbits and are therefore 
depositing coarse material upon the bottom where it is less 
effectively moved. This argument loses much of its force be- 
cause Cornish takes no account of the fact that on a smooth 
bottom the oscillatory motion of the water particles is backward 
and forward in a horizontal plane, the vertical currents upon 
which the validity of his theory depends being absent. Im- 
mediately above the bottom the vertical element of the oscil- 
lation begins to appear, and material carried upward a sufficient 



92 



CURRENT ACTION 




WAVE CURRENTS 93 

distance by eddies due to inequalities of the bottom might be 
somewhat affected in the manner described. 

If we turn our attention for a moment to the action of normal 
waves of translation, we have to note that the currents which 
they produce constitute essentially one intermittent current 
acting in a uniform direction. The water particles, from the 
surface to the bottom, move forward and then stop, the process 
being repeated with the passing of every such wave. Accord- 
ingly the debris on the bottom is always urged forward; and 
since these waves usually come on-shore, they give rise to a 
landward progress of all movable material, both fine and coarse. 
Russell attributes the shoreward transportation of shingle and 
wreck to the action of waves of translation 10 . It appears cer- 
tain that either waves of translation or oscillatory waves may, 
under proper conditions, effect a very remarkable transport 
of debris toward the land; for Murray 11 has shown that shingle 
and chalk ballast dropped into the sea off Sunderland at a dis- 
tance of 7 to 10 miles from land, where the water is from 10 
to 20 fathoms deep, are thrown on shore by storm waves; and 
Gaillard quotes Robinson as authority for the statement that at 
Madras, during a violent storm, a quantity of pig lead, which 
proved to have come from a vessel wrecked more than a mile off- 
shore 12 , was cast upon the beach. The landward transport of large 
cobblestones from deep water far offshore is often effected " not 
by the simple impulse of the currents or storm waves, but by 
such action combined with the buoyancy given to the stones by 
the growth of seaweed attached to them " (Plate X), as was 
pointed out by Kinahan 13 many years ago. Shaler 14 believes that 
some shingle beaches receive their entire supply of material in 
this manner. In the waves produced experimentally by Caligny, 
which combined a translatory movement of the water with an 
oscillatory movement, particles on a level bottom were trans- 
ported in a direction opposite to that of the wave propagation 15 ; 
but we have no sufficient evidence that waves of this type are 
common in nature. 

When a wave breaks at the foot of a beach slope, the water 
which is driven up the slope, forming the swash, carries material 
landward, while the backwash tends to transport it seaward again.' 
The landward component of this alternating current is as a whole 
the stronger, because the return current suffers a loss of ve- 



94 



CURRENT ACTION 



locity due to the friction which acts continuously, and a loss of 
volume due to percolation of the water into the crevices between 
the sand and coarser material composing the beach. Where 
the beach slope is very steep, however, the seaward current may 
be the more effective of the two because it works with gravity, 
while the landward current must propel the debris up the slope 
against the pull of gravity. It should be noted that while the 
swash of the wave, advancing up the beach slope, may retain 
something of the forward component of the true oscillatory motion 
belonging to the wave at the moment of breaking, the backwash 
is really an hydraulic current containing no element of true wave 
motion. 

Beach Drifting. — If waves break obliquely upon a beach, there 
results a very important longshore transportation of debris on 
the beach slope itself. To distinguish this phase of shore activity 




Fig. 13. — Section of beach slope showing by dotted lines the so-called 
zig-zag path of debris particles during beach drifting and by solid lines 
the parabolic paths actually followed. ] 



from the longshore transportation effected by currents in the water 
just outside the beach, I propose to call it beach drifting (" Strand- 
vertriftung" of Krummel, " Kustenversetzung " of Philippson). 
Conformable to this usage, the longshore transportation which 
takes place in the shallow water seaward from the beach, often 
called " longshore drift," will be termed longshore drifting. The 
terms beach drift and longshore drift will then be restricted to the 
material transported by these processes, both being included 
under the broader term shore drift. In the case of beach drifting, 
the swash of the wave advances obliquely up the slope, continu- 
ing the direction of advance of the wave; but the backwash, 



WAVE CURRENTS 



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96 CURRENT ACTION 

being under the control of gravity, tends to return directly down 
the steepest slope. As a matter of fact, the control of gravity 
replaces the oscillatory movement of the water gradually instead 
of abruptly, with the result that the water does not advance 
in an oblique straight line to the top of the beach slope and then 
descend in a straight line at right angles to the shore, describing 
the zig-zag path shown by the dotted lines in Figure 13, but 
rather describes a series of parabolic curves as shown by the 
solid lines. It follows that a pebble under the influence of such 
wave action does not strictly speaking, pursue a zig-zag course 

along the beach as is usually stated, 
but rather a course represented by par- 
allel parabolas. Palmer 16 was the first, 
so far as I am aware, to call attention 
to the importance of this phase of 
wave activity in causing a longshore 
transportation of debris; but his figure 
illustrating the process of beach drift- 
ing incorrectly represents a zig-zag 
path for the transported material, and 
contains a still more serious error in 
that it represents the swash as carry- 
ing both large and small particles an 
Fig. 14. -Parabolic paths of equal distance up tne beach slope, al- 
arge an sma par ic es ^ noU g. n ne rec0 p- n i Z ed that small par- 
of debris subject to beach & °, ^ 

drifting. tides were carried farther down the 

slope by the returning backwash. 
Figure 14 illustrates the fact that small particles describe bigger 
parabolas than larger debris, and therefore progress along the 
beach with greater rapidity. 

The positions of the parabolic paths taken by the particles in 
beach drifting usually depend upon the combined action of more 
than one set of waves, as when the surf and a superposed set of 
wind waves strike the beach at different angles. Even if the 
surf breaks parallel to the beach there will be some beach drifting 
if the wind waves arrive at an oblique angle; but, as shown by 
Figure 15, the angle of advance of the water up the slope will not 
be as oblique as if determined by the wind waves alone, since the 
path actually taken is the resultant of the impulses given by both 
waves. A longshore tidal current, or any other current parallel 




WAVE CURRENTS 97 

to and near the shore, may combine with waves which break 
directly on shore to give a very pronounced beach drifting in the 
direction of the current. With a longshore current moving in a 
direction opposed to that of the oblique waves, sand may travel 



Fig. 15. — Parabolic paths followed by debris particles impelled by the 
combined action of onshore swells (broken lines) and oblique wind 
waves (solid lines). After Kriimmel. 

with the current and coarser material with the beach drift, as was 
fully recognized by Owens and Case 17 . 

The direction of beach drifting will depend upon many fac- 
tors. Among these may be noted the direction from which the 
groundswells approach the shore, in those cases where they are 
not sufficiently refracted to strike the beach at right angles, and 
in which wind waves are on the whole less powerful in determin- 



98 



CURRENT ACTION 




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WAVE CURRENTS 99 

ing the movement of shore debris. Another important factor is 
the direction of the prevailing winds, or of the dominant storm 
winds, in case these develop waves of considerable power, and 
the groundswells are weak, or do not approach the shore obliquely. 
The direction of the greatest stretch of open water is likewise 
important, since weak winds blowing over a long stretch of 
water may develop larger waves than strong winds which cross 
a limited water area. A good example of the effect of " length 
of fetch" is found in the beach drifting along the sandspit 
which encloses Toronto Harbor on Lake Ontario. Here the 
movement of the beach material is westward against the prevailing 
westerly winds, because the greatest stretch of water over which 
westerly winds can blow is 40 miles, whereas easterly winds cross 
180 miles of the open lake surface 18 . Failure to recognize the 
important relation of beach drifting to the direction of greatest 
expanse of open water has led many authors to unsound con- 
clusions, a typical example being Haupt's arguments against 
the efficiency of beach drifting along the New Jersey and other 
shores based on the assumption that if there were any effective 
beach drifting it would have to move with the prevailing winds 19 . 
Haupt cites the well known fact that on the Great Lakes 
material may be drifted in opposite directions from some point 
near the middle of one side of a lake, and concludes this is suffi- 
cient proof that wind waves cannot be responsible for the move- 
ment. An inspection of Figure 16 will suffice to show that this 
conclusion is not justified. Since the dominant waves (shown by 
heavy lines in the figure) depend upon length of fetch as well as 
upon intensity and duration of the wind, it is evident that beach 
drifting between a and c will be southward; because the winds 
from the northeast, blowing across a broad stretch of open 
water, will generate more powerful waves than the winds from 
the southeast which traverse a shorter stretch of water, or the 
much more important prevailing winds from the southwest which 
blow directly off the land. Beach drifting from a to c is thus 
opposed to the direction of the prevailing winds. For similar 
reasons the material north of a is drifted in the opposite direction, 
toward b ; and on the east side of the lake material is drifted in 
opposite directions from d. The expectable directions of beach 
drifting derived theoretically in the accompanying diagrams 
(Fig. 16) appear to correspond with the actual directions re- 



100 



CURRENT ACTION 






Fig. 16. — Diagram to illustrate relation of beach drifting to wind directions 
in an ideal case and in the case of Lake Michigan. The first two figures 
show the relative intensities of oblique wave action and the direction of 
beach drifting on the western and eastern sides respectively of an ideal 
lake with winds blowing from all quarters. The third figure shows 
reported direction of beach drifting along the shores of Lake Michigan. 



. 



WAVE CURRENTS 



101 



ported for Lake Michigan 20 , a lake somewhat similar in form to 
the ideal lake of the figure and similarly situated with reference 
to the prevailing winds. On Lakes Erie and Ontario Wilson 21 
finds a similar relation between direction of beach drifting and 
length of fetch of open water. A proper appreciation of this 
simple principle will enable one to understand many disputed 






Fig. 17. — Parabolic paths of debris particles subject to beach drifting on 
(a) a prograding beach, (6) a retrograding beach, and (c) a graded beach. 



points regarding the movement of shore debris on irregular sea 
coasts. 

Beach drifting may occur on a prograding beach, on a ret- 
rograding beach, or on a beach which is at grade, i.e., one 
which is neither losing nor gaining material. On a prograd- 
ing beach the relation of slope to volume and velocity of the 
alternating currents is such that particles advance farther than 
they retreat, and the ideal path of a single particle is represented 
by Figure A7.Q. The paths which particles on a retrograding 



102 



CURRENT ACTION 




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WAVE CURRENTS 103 

beach and on a graded beach would. tend to take are shown at 
b and c of the same figure. 

The so-called " zigzag " progression of particles of debris is 
commonly treated in connection with beach drifting only, as 
though this type of movement were restricted to the zone of 
breaking waves on the shore. Cornaglia 2 was right, however, 
in ascribing such a movement to debris on the sloping bottom 
seaward from the beach during the passage of unbroken oscil- 
latory waves in a direction oblique to the slope. On the bottom 
the motion of the water particles, as we have already seen, tends 
to be in a straight line, back and forth. With waves oblique 
to the slope this bottom movement (called " flutto di fondo " 
by Cornaglia) would carry the material obliquely up and down 
the slope over the same path, with a general advance or retreat 
in the same straight line when onshore or offshore components 
prevailed, were it not for the effect of gravity. Under the in- 
fluence of this force both water particles and transported debris 
tend to return more directly down the slope after each forward 
oscillation, with the result that a progressive motion, parallel 
to the shore, is added to the back and forth movement. Or, 
in common parlance, the particles " pursue a zigzag path " 
(more properly a series of parabolic curves) on the sea-bottom, 
which results in longshore drifting of a "type analogous to beach 
drifting. 

We shall find in later chapters that many shore forms com- 
monly attributed to tidal and other currents are more reasonably 
to be interpreted as the product of beach drifting. The water 
movements involved in beach drifting have a high velocity and 
hence a great transporting power; and one may readily observe 
coarse debris carried along the coast by their force when tidal 
and other currents are too weak to move anything but the 
finest sands. Shaler has watched pebbles made from ordinary 
bricks move along the shore at the rate of more than half a 
mile a day under the influence of beach drifting, and Wheeler 23 
observed half bricks carried 25 to 30 yards in from 1J to 2 hours 
by the same force. 

Hydraulic Currents due to Waves. — Thus far we have been mainly 
concerned with those currents which are more or less directly in- 
volved in the normal oscillatory or translatory motions of the water 
particles in waves. We must now turn our attention to the hy- 



104 CURRENT ACTION 

draulic currents, which are the indirect product of wave action. It 
has already been shown that with every wave of translation there 
is a direct shoreward movement of the water, which is not com- 
pensated by a backward movement. Hence a series of such waves 
coming onshore tend to pile up the water above the normal level 
of the sea. Since oscillatory waves entering shallow water are 
partially transformed into waves of translation, they too must 
cause accumulation of wa er against the coast. Even were they 
not thus transformed, the slight excess of the shoreward com- 
ponent in waves of oscillation which has already been described 
would have a tendency in the same direction. Thus on- 
shore waves raise the level of the sea along a coast upon which 
they break. An appreciable local rise in the sealevel due to 
this cause has been inferred by several writers 24 and has been 
demonstrated by the author at certain points along the Atlantic 
Coast. 

It is clear that the water piled up against a shore in the man- 
ner just described must escape, thereby producing more or less 
continuous " hydraulic currents." If the escape is seaward, 
along the bottom, we have the current known as the undertow; 
if the escape is effected by currents moving along the shore away 
from the area of accumulation in either direction, we have a 
longshore current, sometimes called " longshore drift." The 
undertow may temporarily be checked under each wave crest, 
and may even have its direction momentarily reversed by the 
forward moving water of that part of the wave; but under the 
wave trough the undertow combines with the backward moving 
component of oscillatory waves to form a seaward bottom cur- 
rent of great strength. A marked development of the under- 
tow is favored by oscillatory waves, for these disturb the bottom 
waters less than the surface; by a broad zone of waves striking 
a long stretch of the shore at right angles, since these con- 
ditions are unfavorable to the ready escape of the water as 
longshore currents; and by a steep offshore bottom and deep 
water close to shore, because the returning water is then enabled 
to pass quickly down beneath the disturbed surface and move 
seaward with little interruption. Longshore movement is 
favored by waves of translation, since waves of this class give 
a vigorous shoreward motion to all the water from the surface 
to the bottom; by an oblique angle of wave incidence, because 



WAVE CURRENTS 105 

water propelled obliquely against a shore tends to produce a 
strong current in the general direction of the propulsive force; 
and by gradually shallowing water offshore, which favors the 
development of waves of translation and a shoreward movement 
of the water at all depths. 

Work of Wave Currents. — We must conclude from what has 
been said in the preceding paragraphs that waves are profoundly 
important as agents of erosion and transportation, both on shores 
and shallow bottoms. It is not easy to understand the process of 
reasoning which led Lieutenant Davis to ignore the more important 
activities of wave currents in his memoir on the various currents 
of the ocean, and to conclude that " the most noted and interesting 
effect of waves is the ripple-mark" 25 . The careful reader of his 
memoir will discover that many of the phenomena ascribed by 
Davis to tidal action are more probably the effects of wave cur- 
rents. In like manner Kinahan 26 reaches the conclusion that wind 
waves do very little permanent work. He ascribes to tidal 
action beach drifting and other phenomena undoubtedly pro- 
duced by wave action. 

It is also evident from the foregoing paragraphs that the 
action of wave currents upon debris varies greatly under dif- 
ferent conditions. On a flat bottom oscillatory waves will move 
debris prevailingly shoreward; but if the slope be steep enough, 
the same waves may cause material to migrate seaward; or 
coarse debris may be propelled shoreward and fine debris sea- 
ward. If the waves belong to the class of true waves of trans- 
lation, the debris will be transported landward, even on a sloping 
bottom. Waves breaking on the beach drive material up the 
slope until continued accumulation makes the slope so steep 
that the backwash returns all material to the breaker zone. If 
the beach slope is too steep for a given set of waves, the back- 
wash will return more material than was brought by the for- 
ward rushing current, and the beach will suffer erosion. Beach 
drifting will vary in direction and amount with changes in the 
direction and size of the waves. The seaward component of 
wave motion may be effectively supplemented by the undertow. 
If the undertow is strong it may prevail over the landward com- 
ponent of wave motion, and cause the bottom debris to move 
continuously seaward; but if the waters piling up against a 
coast escape laterally as longshore currents, the debris may 



106 



CURRENT ACTION 



first move landward, and then suffer some longshore trans- 
portation under the influence of these currents. Since the several 
types of wave currents vary in strength with the outline of the 
shore, the angle of offshore slope, the angle at which the waves 
approach the shore, the size of the waves, and the kind of waves, 
it is manifest that the analysis of wave action upon shore debris 
is no simple matter. This conclusion is amply justified by the 
experience of those engineers who have studied the effects of 
waves on natural shores and artificial structures. Gaillard 27 ex- 
presses the general opinion of the profession when he says " In 
scarcely any branch of engineering are the forces developed 
and the methods and directions of their application more vari- 
able than in the case of wave action." Before pursuing this 
point further, let us proceed with our inquiry into the behavior 
of other types of currents. 

Tidal Currents. — The tides may best be considered as great 
waves which combine some of the features of both oscillatory 



High Tide 




Fig. 18. — Elliptical orbit of water particle during passage of the tide wave 
over a sloping sea-bottom. 



waves and waves of translation 28 . They resemble oscillatory 
waves in having an orbital motion of the water particles, the 
orbit becoming a very much flattened ellipse in the shallowing 
water, with its long axis rising toward the land (Fig. 18). 
As will appear from the figure, there is a shoreward movement 



TIDAL CURRENTS 107 

of the water particles until near the time of high tide, after which 
a seaward movement takes place. These orbital movements of 
the water constitute tidal currents. Immediately at the shore 
the landward or " flood current " may continue to flow until 
the very moment of high tide. In the open sea, or in the case 
of tides passing a headland projecting far out to sea, the orbital 
path would not be distorted as in Figure 18, but would be more 
nearly circular; hence it is clear that the landward movement 
would persist for a long time after high tide, just as the forward 
motion of the water particles in an oscillatory wave continues 
after the wave crest has passed (Fig. 1). 

The great importance of these tidal currents may readily be 
appreciated from a consideration of their velocities. Krummel 
has shown that in water 30 meters deep a tidal rise of 3 meters 
should result in currents having a velocity of 1.7 knots per hour; 
and with a rise of 4.5 to 6 meters the currents should attain a 
velocity of over 3 knots per hour. The observed velocities are 
in agreement with the theoretical deductions. According to 
Wheeler tidal currents in the English Channel between Scilly 
and Hastings have a velocity of 2 miles * an hour; in the northern 
part of the Wash, 4 miles; and off the island of Ushant, France, 
6 to 7 knots per hour 29 . In St. Malo Bay where there is a rise 
of 10 to 12 meters and a water depth of 30 meters, the velocity 
of tidal currents is from 5.1 to 6.7 sea miles per hour 30 . At 
Hell Gate in New York Harbor the currents attain a velocity 
of 4.8 knots per hour 31 while Bailey reports a current of " not less 
than 8 knots " through the Petite Passage southwest of Digby 
Gut, Nova Scotia 32 . Stevenson gives the velocities of a dozen 
tidal currents which vary from a minimum of 5.75 to a maximum 
of 12.20 statute miles per hour 33 . Sollas states that the tides 
in the Severn estuary have a velocity of from 6 to 12 miles an 
hour 34 , while Krummel cites velocities of 8 to 10 knots between 
the Orkney and Shetland Islands, 11 knots in the dreaded 
" Roost " of Pentland Skerries, and 11 J knots in the Gulf of 
Hangchau 35 . 

* It has seemed wisest to give velocities in the units originally employed 
by the various authorities, as any attempt to convert the expressions into a 
standard unit of measurement would in some cases introduce a misleading 
appearance of accuracy if fractional parts of the unit were employed, and in 
other cases would introduce large errors if the fractions were ignored. 



108 CURRENT ACTION 

The transporting and eroding power of such currents is enor- 
mous. A velocity of but .4 knot per hour will drive ordinary 
sand along the bottom, while fine gravel will be moved if the 
velocity rises to 1 knot; shingle about an inch in diameter is 
moved at 2.5 knots; and angular stones about one and one-half 
inches in diameter, at 3.5 knots 36 . Inasmuch as tidal currents 
continue for many miles in the same direction, it is evident that 
they must play a very important role in the transportation of 
shore debris and in submarine denudation whenever the velocity 
approaches the higher figures mentioned above. 

G. H. Kinahan describes a number of beaches and submarine 
banks on the coast of southeast Ireland which he believes were 
formed mainly by tidal currents 37 . H. C. Kinahan states that 
sands and gravels in " Beaufort's Dyke " off the coast of the 
Mull of Galloway are moved back and forth by currents gen- 
erated by the combined action of tides and waves at a depth of 
720 to 860 feet 38 . Along the deeper middle portion of Long 
Island Sound the mean velocity of the tidal inflow is nearly 1 
meter per second and of outflow slightly less, or high enough 
to transport coarse gravel. Dana shows that wherever there 
is any narrowing of the Sound by shoals or islands there is an 
increase in depth, and he attributes this to increased erosive 
force of currents at these points. He finds such effects to a 
depth of 330 feet 39 . In a paper discussing " Erosion durch 
Gezeitenstrome " Krummel expresses the opinion that this 
agency is responsible for the fact that whereas the floor of the 
Bay of Fundy usually has a depth of from 50 to 70 meters or 
less, depths of from 100 to 110 meters occur where the tidal 
currents are restricted by the narrows at Cape d'Or and Parrs- 
boro 40 . Reade ascribes to tidal scour the formation of trenches 
between islands off the coast of Scotland having depths of 
nearly 800 feet 41 ; but the possibility that these trenches repre- 
sent submerged subaerial valleys should not be overlooked. 
The strong tidal currents of the Severn sweep along great masses 
of boulders thereby deepening the channel, according to Sollas; 
and Richardson attributes the deep water known as the " shoots " 
to this erosive action 42 . Sections taken along the deep-water 
channel of the Hooghly River in 1813 and 1836 showed that 
between those years tidal currents had scoured out the silt of 
the river bed to a depth of 52 feet, forming a " scour hole " 



TIDAL CURRENTS 109 

20,000 feet long at the top and 9000 feet long at the bottom 43 . 
Helland-Hansen 44 has shown that marked tidal currents exist 
at the bottom of fairly deep oceanic waters. On the Michael 
Sars Expedition, which made the first measurements of such 
currents in deep water, he found a true tidal movement of .27 
meter per second (more than .5 knot per hour) at a depth of 
732 meters, or 2400 feet, south of the Azores. Krummel 45 
admits the efficiency of tidal currents in sweeping rocky ridges 
free of mud at a depth of 6500 feet or more. When it is re- 
membered that a current of .20 meter per second or .4 knot per 
hour will transport ordinary sand, it is clear that tidal currents 
may transport coast debris to great depths and under favorable 
conditions may even effect some erosion far below the surface 
of the ocean. Gardiner 46 has gone so far as to attribute the 
submarine plateau of the Maldives to the action of planetary 
and tidal currents in cutting down a land area to a depth of 
1140 feet below sealevel; but while the theoretical possibility of 
such erosion must be admitted, the evidence on which Gardiner 
bases his conclusion in the Maldive case is not convincing. 

Tidal currents do not always, or even commonly, act in a 
direction normal to the shoreline. Along the sides of a bay or 
headland whose axis is in the line of tidal advance, the current 
may be parallel to the shore. Shoreline irregularities will de- 
flect the tidal waters, giving longshore currents in all possible 
directions. These longshore currents are commonly much 
swifter than those movements which take place normal to the 
beach. On an open coast, exposed to the direct advance of 
the tidal wave, the onshore and offshore movements of the 
water are very weak, and can accomplish very little geological 
work, as can readily be verified by the observer on such a coast 
during a calm day. On the other hand, longshore currents close 
to the land are very effective geological agents, since they remove 
the debris produced by wave erosion and brought to the sea 
by rivers, transport it to distant localities, and often deposit 
much of it in deep water. They may even produce profound 
changes along the shores by direct erosion, as in the case of the 
violent currents associated with the bore in the estuary of the 
Amazon, the effects of which have been well described by Bran- 
ner 47 . The currents which pass up and down a bay or estuary 
are here considered longshore currents; for while they may be 



110 



CURRENT ACTION 




TIDAL CURRENTS 111 

normal to the general trend of the outer coast, they are in general 
parallel to the immediately adjacent shores. 

It is a well known fact that a narrowing bay compresses a 
tidal wave into smaller space and constrains it to rise higher. 
Thus we get the remarkable tidal rise at the head of the Bay 
of Fundy and in the River Severn. It is likewise true that 
when the energy of the tidal wave is transmitted to the smaller 
volume of water in front, the effect on the latter is correspondingly 
great. The smaller volume of water develops a swifter current 
and piles up higher against the coast. If the form of the coast 
prevents the escape of the accumulated waters laterally, they 
will continue to rise until the head counterbalances the momen- 
tum of the advancing current. On the other hand, if a large 
bay is separated from the open ocean by a narrow inlet, practi- 
cally no true tidal motion takes place within the bay. The tidal 
wave is scarcely transmitted through the narrow channel, and 
the water within the bay rises because of the hydraulic head 
resulting from the accumulation of water against the coast out- 
side. Such currents as result from the rise and fall of the water 
within the bay are really hydraulic currents, and are not parts 
of any true oscillatory movement of the water. 

In bays and sounds the swiftest tidal currents follow the 
deepest channels, and are therefore not as directly effective in 
shore processes as when they impinge upon an exposed portion 
of the coast. Even here, however, they have an indirect effect 
of no mean importance; for they remove vast quantities of 
debris, which was originally eroded from the land by wave action 
or carried to the sea by rivers, and then transported by longshore 
currents of different types until brought within the influence of 
the inflowing or outflowing tidal current. The inflowing tide 
sweeps the finer material far up the bay where it is deposited 
in mud flats and tidal marshes, which are often reclaimed for 
cultivation by the process known among the English as " warp- 
ing " 48 , while the coarser sand is moved landward a much shorter 
distance, often forming bars along the channels. The outflowing 
current carries the material it receives out to sea, and shifts 
the bars in the same direction. Because of the river water 
usually poured into a bay the ebb current predominates over 
the flood, and the direction of debris migration is prevailingly 
seaward. The net result of this current action, therefore, is to 



112 



CURRENT ACTION 




.2 ° 

fcJD g 
CD G 

> 2 

II 

_C2 ^ 



s/ 



O 



TIDAL CURRENTS 113 

favor wave erosion by removing debris to deep water, thus 
keeping the shores better exposed to renewed attacks. 

Deposition by Tidal Currents. — The great importance of in- 
coming tidal currents in bringing about local deposition at the 
heads of bays and in the quiet waters of harbors justifies further 
consideration of this point. There is a tendency to ascribe to 
the deposited material a fluvial origin, and many have argued 
that only the rivers entering the bay are capable of bringing so 
much fine sediment to the place of deposition 49 . But Skertch- 
ley 50 has shown that the rapid silting up of the Wash in eastern 
England, by which a breadth of three miles has been added to 
the land in some places since the Roman occupation, is accom- 
plished by the sea and not by rivers. Deposition occurs mainly 
at the slack of high water, although a little of the material settles 
in sheltered places during the ebb. Crosby 51 ascribes the deposi- 
tion of silt in Boston Harbor to the action of incoming tidal 
currents, and shows that the Mystic River, which enters the 
harbor, has effected scarcely any deposition in the lakes through 
which it flows during the same period of time in which a maxi- 
mum of 25 feet of the silt has accumulated in the harbor. 
Mitchell 52 is of the same opinion "regarding detritus underlying 
salt marshes on other parts of the New England coast. The 
extensive deposits of red silt at the head of the Bay of Fundy 
are largely due to the action of the strong flood tide which carries 
in the material eroded from the shores of the bay 53 . In his 
excellent study of the Severn estuary Sollas 54 has demonstrated 
that the flood tide not only brings in large quantities of silt but 
also innumerable remains of marine organisms which are de- 
posited with the silt in the upper reaches of the main estuary 
and in the tributary estuaries. According to Browne 55 this de- 
position takes place not only at the slack water of high tide, 
but during two-thirds of the ebb tide, since he found that in the 
Avon below Bristol the silt-laden lower waters remain stagnant 
long after the surface waters have begun to ebb. 

It should be appreciated, however, that even where extensive 
deposits of silt are laid down by tidal action at the heads of 
bays, these same tides transport much material far out to sea, 
where it comes to rest in deep water. On a subsiding coast the 
amount of material deposited at the bay head may exceed that 
carried seaward; and if the subsidence gives place to stability 



114 ] CURRENT ACTION 

this excess of deposition may continue for a time, until the heads 
of the drowned valleys are well silted up. In time, a condition 
of approximate equilibrium will be approached, when the swifter 
tidal currents of the narrowed channels will erode about as much 
material as they deposit. From that time onward the material 
brought out by rivers and eroded from the shores by waves will 
add little if anything to the extent of the tidal deposits. The 
tidal currents charged with sediment will sweep up and down the 
bay, depositing in one place and eroding in another, depositing 
at slack water and eroding at times of swiftest flow; but each 
retreating tide, re-enforced by the outflowing river water, will 
remove from the bay an amount of material equivalent to that 
brought in by various agencies. According to Sollas the Severn 
estuary has reached this nicely balanced condition, in which 
" the accumulation is always being diminished by withdrawals 
seaward, and as constantly renewed by fresh accessions provided 
by the denudation of the land " 56 . The Wash appears not to 
have reached this stage of equilibrium, for, as described by 
Skertchley 57 and observed by the present writer, the deposition 
far exceeds the removal of material and the land gains upon the 
sea. Along the head of the Wash the average rate of gain was 
7.29 feet per year from the second to the seventeenth centuries, 
48.65 feet per year during the eighteenth century, and 31.68 feet 
per year during the nineteenth century 58 . It would seem reason- 
able to suppose that with a gradual decrease in the supply of 
sediment furnished to the tidal currents, an area of tidal de- 
posits might pass beyond the stage of equilibrium and enter a 
stage in which more material was eroded from the region than 
was returned by the incoming tide. It is possible that the head 
of the Bay of Fundy has entered this last stage, for in several 
localities visited by me no appreciable accumulation had taken 
place since the last dykes were built, and in one locality consid- 
erable erosion had evidently occurred, uncovering the ancient 
forest described by Dawson in his Acadian Geology 59 . Perhaps 
an excess of erosion over deposition is also responsible for the 
abandonment of certain tide marsh areas and for the increased 
difficulty of maintaining the dykes; facts for which Dawson 
suggested a change in the direction of tidal currents as one of 
several possible explanations 60 . A careful examination of older 
and later surveys of regions about the head of the bay might 



TIDAL CURRENTS 115 

possibly determine the validity of the explanation here tenta- 
tively suggested. 

In the case of a bay which receives little or no river water the 
tidal regime may be such that the flood currents prevail over the 
ebb at all times. Deposition will then exceed erosion, not 
merely until the regions adjacent to the main channels are 
silted up, but the channels may themselves be blocked and the 
tides completely excluded from the former bay by their own 
deposits. This fact led Browne to the conclusion that tidal 
deposition always exceeds tidal erosion, and that therefore when 
no river water flows through a tidal creek or bay to keep the 
channels scoured out, such an area must in time silt up entirely 61 . 
The arguments used to support his conclusion are not convincing, 
and it is probable that whether or not deposition exceeds erosion 
in such a bay or creek will depend on the nature of the tidal 
wave entering the depression and the nature of the currents to 
which it gives rise. Both vary greatly under different conditions, 
and there is no theoretical reason, at least, why the tidal regime 
may not be such as to favor erosion more than deposition in 
some cases, deposition more than erosion in others. 

Movement of Debris by Tidal Currents. — The seaward journey 
of sediment held in suspension by tidal currents in an estuary 
or tidal river is far from simple. Even if we leave out of con- 
sideration the shorter or longer halts made by a given particle, 
and imagine it to be continually in transit, the ebbing and flow- 
ing tides carry it back and forth over the same ground many 
times, greatly prolonging its journey. Because the " land water " 
poured into the estuary by rivers causes the ebb tide to pre- 
dominate over the flood by a greater or less amount, the particle 
is carried seaward by each ebb a little farther than the following 
flood carries it back; and so it gradually makes its way farther 
and farther toward its final resting place in deep water. An 
exception to this occurs temporarily in some estuaries where the 
resultant is landward while the spring tides are strengthening; 
but this temporary upstream progress gives place to a more pro- 
nounced seaward advance after spring tides are past. Numerous 
experiments with nearly submerged floats have demonstrated 
the predominance of the seaward component in such tidal oscilla- 
tions. Figure 19 shows the course taken by such a float in New 
York Harbor, where the Metropolitan Sewerage Commission has 



116 



CURRENT ACTION 




L o w s e r Bay 



Finish 



Fig. 19. — Course followed by a nearly submerged float under the influence 
of tidal currents in New York Harbor. (After Parsons.) 



TIDAL CURRENTS 



117 



studied the effect of tidal currents on the transportation of 
sewage. Figure 20 shows the theoretical path during successive 
tides, which a particle would take on this same journey, and it 
will be seen that the theoretical and actual paths agree closely. 
Both demonstrate the seaward migration of particles in suspen- 
sion. The comparative volumes of the ebb and flood currents, 
responsible for this seaward migration, may be seen in the follow- 
ing table taken from a paper by Parsons 62 . The importance of 
river water in augmenting the ebb is clearly apparent from this 
table. 

VOLUMES FLOWING ON EBB AND FLOOD CURRENTS, 
HARBOR OF NEW YORK, IN MILLIONS OF 
CUBIC FEET 





Yearly means 




Ebb 


Flood 


The Narrows 


12,041 
7,430 
6,990 
6,230 
3,980 


10,779 
6,343 


Hudson River, off the Battery 


" " 39th Street 


5,903 
5,143 

2,893 


" Fort Washington Point 

" " Tarrytown 





In branches of the harbor where little land water enters, the 
difference between ebb and flood volumes is not so great. In 
other harbors where larger rivers than the Hudson enter, the 
difference must be much more marked. Experiments with 
floats in the Thames estuary show that the average seaward 
progression of a particle in suspension is J mile a day 63 . 

One result of the back-and-forth journeying of each particle 
is the accumulation in estuaries and tidal rivers of a vastly 
greater amount of material than is daily contributed to their 
waters. " Thus in the waters of the Severn estuary there is a 
storage of suspended sediment, the accumulation of as many 
days, or weeks, or months as are occupied in its wanderings to 
and fro " 64 . 

There may be some question as to whether the coarser material 
on the bottom of estuaries and tidal rivers always has a tendency 
to move prevailingly seaward. Such material is certainly 
shifted back and forth by the ebb and flood currents, as shown 



118 



CURRENT ACTION 



25 



15 s 



in the case of a sunken vessel at the mouth of the Gironde which 

had the sand scoured 
from about it by the 
ebb current and was 
completely buried 
again by the flood 
current 65 . Experi- 
ments with floats 
show the predomi- 
nance of the seaward 
component of tidal 
oscillations at or near 
the surface of the 
water, but do not tell 
us about the move- 
ments in depth. It 
seems probable, how- 
ever, that there is 
ordinarily a similar 
seaward tendency in 
the deeper waters also. 
The seaward compo- 
nent of the oscillation 
has a further advan- 
tage in that it works 
with gravity ; for par- 
ticles of sand will 
travel farther down 
the slope of the chan- 
nel with the ebb than 
they will up the slope 
with a flood current 
of equal velocity and 
duration. But three 
factors at least tend 
to give an advantage 

Fig. 20. — Theoretical course calculated by Par- ^ ^e flood current 

sons for the float whose actual course is , "• rru 

, . ■_. 1A in certain cases, lne 

shown in Figure 19. 

waters of a bay are 
often much fresher than those of the ocean, because of dilution by 



Mt. St. Vincent 


r\ 












































Grants Tomb 












— tr- 










































c 












I 














The Battery 


















































































\ 












































'\ 






\j 
















f 


\ 


Sandy Hook Beacon 


















r\ 






u 




^ 












Scotland Lightship 
































J 


\J 





TIDAL CURRENTS 119 

rivers. Heavier salt water from the ocean may therefore push in 
along the bottom while the surface waters are still flowing sea- 
ward 66 . This action will be facilitated by differences in tempera- 
ture, if the waters of the bay are warmer than those of the ocean 67 . 
Mitchell has shown that at the mouth of the Hudson River the 
bottom water moves landward with a velocity of .6 meter per 
second, or more than 1 knot per hour, while the surface waters 
are still ebbing 68 . During part of the ebb tide, therefore, trans- 
portation of bottom debris may be landward. Furthermore, 
since Browne 69 has shown that the bottom waters may also be 
stagnant during part of the ebb, it would seem possible to have 
a case in which the flood waters entered a bay along the bottom 
during the last of one ebb tide, then remained stagnant while 
the surface flowed back to the sea during much of the following 
ebb. If flood currents thus predominate on the bottom and ebb 
currents at the surface, coarser material will migrate landward 
while material in suspension is carried seaward. Mitchell was 
of the opinion that the flood does predominate in New York 
Harbor below a depth of 6 fathoms 70 , and that it would cause 
the bar at the harbor mouth to advance up the channel, were 
this action not prevented by other currents 71 . As the coarser 
material of a landward moving deposit is ground to a finer size, 
however, it will rise in suspension and move seaward toward the 
ultimate goal of all land debris — quiet, deep water. 

A second factor favoring the landward movement of bottom 
debris arises from the change in form which the tidal wave some- 
times experiences when entering a bay or tidal river. The front 
of the wave becomes steeper than the back, and the flood current 
is much stronger than the ebb, the latter lasting a longer time. 
An extreme case of this inequality of current velocity is found 
in the tidal " bore " or " eager " which invades certain rivers, 
notably the Tsien-Tang-Kiang of China, where the front of the 
wave sometimes appears as a wall 25 feet high, and a million 
and a quarter tons of water may be carried by a given point in 
one minute 72 . The vigorous current of the " pororoca," or bore 
of the Amazon River, has already been mentioned 73 . Under 
such conditions bottom debris which is entirely too coarse to be 
affected by the longer continued but weaker ebb current may be 
carried forward by the flood. It would seem, therefore, that 
conditions may exist which compel a landward migration of 



120 CURRENT ACTION 

bottom debris under the influence of tidal currents, although this 
material when ground finer would move seaward under the same 
tidal regime. A sufficient body of observations is not yet avail- 
able to enable one to determine how widespread these conditions 
may be. 

Where beach deposits above mean sealevel are subject to 
transportation by tidal currents, either with or without the aid 
of wave currents, there may be a marked tendency for such shore 
debris to migrate in the direction of the flood current. This 
arises from the fact that where the tide flows freely, high water 
coincides more or less closely with the flood and low water with 
the ebb. Hence those beach deposits above mean sealevel will 
be moved by the flood current, but will not be reached by the 
ebb current. In bays and inlets this striking difference in the 
efficiency of flood and ebb currents in transporting beach material 
is less marked than opposite headlands, because near the bay 
heads flood begins when the tide is lower and ebb commences 
soon after high water is attained. It follows, therefore, that the 
debris which migrates along the shore from the headlands toward 
the bay heads under control of the dominant flood must come to 
rest where flood and ebb more nearly neutralize each other. 
This should give rise, in the absence of counteracting influences, 
to a tidal accumulation of debris in the heads of bays and 
inlets 74 . 

In a bay which has no strong tidal currents, the incoming 
flood may be incapable of stirring up any appreciable quantity 
of sediment, so that little material is carried to the bay heads 
for deposition. On the other hand, the ebb tide augmented by 
the outflow of river water may be sufficiently strong to carry 
into deeper water such sediment as is brought in by the rivers 
or supplied by wave erosion. Under these conditions tidal 
deposits at the bay heads will be conspicuous by their absence. 
The small amount of such deposits at the mouths of rivers enter- 
ing Chesapeake Bay may perhaps be thus explained. 

Along very irregular shores the comparative strength of flood 
and ebb currents can scarcely be predicted. Each area must 
be studied for itself. The positions of channels between islands 
and shoals, with reference to the direction of advance of the 
currents, may be such that some channels will have strong 
flood currents and very little ebb, while others will have vigorous 



TIDAL CURRENTS 121 

ebb currents and scarcely any movement during the flood. 
Bache 75 found the ebb currents near Sandy Hook much more 
powerful than the flood, and was indeed of the opinion that ebb 
currents are practically always far more important than the 
flood as eroding and transporting agents. The process of reason- 
ing by which he reaches this conclusion does not seem convincing; 
and while the predominance of ebb currents in bays receiving 
upland waters may be admitted as a general rule, subject to 
certain exceptions, the relative strength of flood and ebb in the 
straits and other channels of an irregular coast must be more 
variable. 

Hydraulic Currents Due to Tides. — The changes in surface level 
of the ocean resulting from tidal action inevitably cause the for- 
mation of various types of hydraulic currents, which we may now 
briefly consider. When the tide rises higher on one part of the 
coast than on another, any part of the water which does not partici- 
pate fully in the tidal oscillation will flow from the higher toward 
the lower level under the influence of gravity. We may thus get 
hydraulic currents having the same periodicity as true tidal cur- 
rents 76 . The waters piled up against a coast by a rising tide may 
escape to either side as longshore hydraulic currents; or if the 
waters are piled up at the head of a converging bay so that lateral 
escape is not possible, there may be developed an undertow which 
will give a seaward motion to the bottom waters before the di- 
rection of the surface current is reversed 77 . 

In the case of a bay separated by a narrow inlet from the open 
sea, the tide in the ocean rises so rapidly that enough water can- 
not pass through the inlet to keep the bay surface rising at the 
same rate. Later the tide in the ocean will fall more rapidly 
than the surface of the bay, because the outflowing water es- 
capes through the narrow inlet so slowly. Consequently the 
ocean surface is highest part of the time, while the bay surface 
is highest at other times. These differences of levels, which 
may amount to a number of feet where the tidal range is large, 
give rise to hydraulic currents into and out of the bay. Such 
currents may have a very steep gradient and correspondingly 
high velocity, as in the case of those at the narrow entrance to 
St. John's Harbor, New Brunswick, where the average maximum 
head is nearly 10 feet, and a reversible fall is produced, facing 
inward when the water in the ocean is highest, and outward 



122 CURRENT ACTION 

when the water in the harbor is highest. Hydraulic currents of 
this type are important features at the inlets connecting the 
ocean with lagoons behind offshore bars along much of the 
Atlantic coast. 

Hydraulic currents greatly complicate the true tidal move- 
ments of coastal waters. An idea of their importance may be 
gained from an inspection of the review of tidal currents for 
different parts of the world given by Harris in his " Manual of 
Tides," where many of the associated hydraulic currents are 
mentioned 78 . According to Parsons the tidal currents in New 
York Harbor vary greatly in character, some being almost 
wholly oscillatory, others almost wholly hydraulic, and the re- 
mainder combining both elements in varying proportions 79 . 
Many, if not most, of the tidal currents observed along a coast 
are compound currents, consisting in part of true oscillatory 
movements of the water and in part of hydraulic movements. 
This is doubtless true of many of the tidal currents whose velo- 
cities are noted on a preceding page. 

Seiche Currents. — The phenomena of seiches have already 
been described. It is evident that the rising and falling of 
water due to seiches in a lake, or in a bay of the ocean, must 
produce currents. As a rule these currents are so feeble in the 
main water body as to be scarcely perceptible; but if the waters 
are compressed into a narrower or shallower space, they may 
acquire an appreciable velocity. If the waters temporarily 
raised or lowered at one end of the basin are connected by a 
narrow strait with another water body, hydraulic currents of 
considerable force may be produced in the strait. The remark- 
able currents in the Strait of Euripus 80 appear to be largely of 
this origin. According to tradition Aristotle plunged into these 
turbulent waters in despair because he could not solve the 
mystery of their movements. The behavior of the water in the 
Strait is enough to justify the tradition, for the seiche currents 
are combined with tidal currents in such manner as to give nearly 
normal tidal movements for several days, followed by another 
period in which the waters ebb and flow twelve or fourteen 
times a day 81 . " The currents . . . are so violent that mills are 
kept in operation by them " 82 . Seiche currents must frequently 
modify tidal and other currents to an extent not yet determined; 
but it does not seem probable that they are often so strongly 



WIND CURRENTS 123 

developed as naterially to affect shoreline processes. Even in 
the Strait of Euripus, Cold 83 was unable to find any effect of the 
seiche currents upon the shores. 

Wind Currents. — When wind blows over water it tends to 
drag the surface particles of the water along with it. Thus 
the water surface acquires a motion in the direction of the wind, 
although the velocity of the water never equals that of the wind. 
Because of the viscosity of water this motion is gradually com- 
municated to the deeper layers but with rapidly diminishing 
intensity. It has been demonstrated that in course of time 
continuous wind action upon an unconfined ocean would set 
the entire body of the ocean in motion 84 . The surface currents 
produced by wind are often spoken of as wind drift, or drift 
currents; but since the term " drift " is also applied to currents 
of almost any origin which happen to flow parallel to the coast, 
as well as to shore detritus which is being moved by such cur- 
rents, and since the terms "drift" and " drifting" are used in a 
restricted sense in this volume, it will be better for sake of 
clearness to employ the term " wind currents " when referring 
to the currents now under discussion. This term is not wholly 
satisfactory, as it suggests rather too strongly the air currents 
which are the cause of the water currents here considered; but 
since air currents cannot properly be called " wind currents," and 
since the term wind currents is analogous to the terms wave 
currents, tidal currents, and seiche currents already used, we 
may continue to speak of wind currents until a better term is 
suggested. 

The velocity of wind currents will depend upon the strength 
of the wind, the length of time it has been blowing, and the 
size and shape of the water body. In the open ocean the sur- 
face waters under the trade winds ordinarily have a velocity of 
from 15 to 25 miles per day. Along the shore a velocity of 
three or four miles an hour during a strong wind is not unknown. 
Harrington 85 reports wind currents on the Great Lakes moving 
from 2 to 3 miles per hour, and Taylor 86 observed a current on 
the east shore of Lake Michigan which moved northward under 
the influence of " a strong sou'wester " with an estimated 
velocity of 4 miles. Currents of such velocities moving over a 
shallow bottom parallel to the shore are doubtless effective in 
the longshore transportation of debris, helping to remove eroded 



124 CURRENT ACTION 

material from the bases of cliffs and river-brought sediment from 
opposite stream mouths, as well as determining the character 
of the shores where their loads are deposited. 

Hydraulic Currents Due to Winds. — Wind currents are ex- 
tremely effective in causing hydraulic currents. If a wind cur- 
rent impinges directly upon a coast, the water is piled up above 
its natural level. In shallow water bodies, or on a shelving shore, 
the rise in level may be very marked, but is slight on steep coasts 
with deep water close in shore. The heaped up waters must 
escape to one side or along the bottom. If the latter mode of 
escape prevails, the seaward moving waters resemble the under- 
tow, and may assist in the removal of fine debris to deep water. 
Such currents are sometimes spoken of as " counter currents in 
depth." Southeasterly winds in summer drive the surface waters 
of the Gulf of California northward toward the head of the Gulf, 
whence there is no opportunity for escape on the surface. At a 
depth of 50 meters the water is found to be moving southward 87 . 
Hunt observed a strong bottom current flowing out of Torquay 
Harbor when a gale drove the surface water inward 88 . 

The reverse of this circulation occurs when winds blow off- 
shore, driving the surface waters out to sea. Bottom currents 
then move in toward the land to replace the water driven away 
by the wind. On the coast of Europe bathers are familiar with 
the fact that the water is warmer when the winds blow toward 
the land and colder when they blow in the opposite direction. 
This is because onshore winds pile the warm surface waters 
up against the coast, and the colder bottom water escapes sea- 
ward; while offshore winds blow the warm water away from the 
coast, and colder bottom water moves in to take its place. The 
northeast trade winds continually blow the surface water away 
from the northwest coast of Africa, with the result that abnor- 
mally cold water is always found near that shore, having moved 
in from the offshore depths 89 . Similar effects are produced in 
winter on the northeast coast of North America by the prevail- 
ing westerlies 90 , and on other coasts which have prevailing off- 
shore winds. Bottom currents of the type here described are 
probably comparatively feeble as a rule; but under favorable 
conditions, as in channels between shallows or in a shallow bay 
where the water blown in can only escape as a thin bottom layer, 
they may have velocities sufficient to move fairly coarse debris, 



WIND CURRENTS 125 

especially if the bottom is agitated by waves which keep the 
debris in suspension. Such debris would then migrate land- 
ward with an offshore wind, and seaward when the wind is on- 
shore. 

Important surface currents result when waters heaped up by 
the wind against a coast escape to either side along the shore, or 
through some strait into an adjacent water body. Water driven 
westward across the Atlantic by the trade winds piles up against 
the western shores of the Caribbean Sea, raising the level of 
the Sea above that of the Gulf of Mexico. There results an 
hydraulic current through the Strait of Yucatan into the Gulf 
which is one of the strongest of known ocean currents, having 
a velocity of 60 to 120 miles a day. The Gulf of Mexico, in 
turn, is higher than the Atlantic Ocean, and hence an hydraulic 
current passes through the Florida Strait into the ocean with a 
velocity of 70 to 100 miles a day. This is the beginning of the 
Gulf Stream proper, which off Cape Florida is only 15 miles from 
the shore and affects the bottom to a depth of nearly 3000 feet. 
" By calculation it has been shown that a current of the velocity 
of the Gulf Stream requires a difference of elevation of at least 
0.7 feet of the Gulf over the Atlantic, which difference agrees 
very nearly with that found by direct leveling across the Florida 
Peninsula " 91 . A line of levels run between Cedar Keys on the 
Gulf coast and St. Augustine on the Atlantic indicates that the 
difference in level is probably at least 0.8 feet 92 . A current of 
11 miles per day flowing eastward through the strait between 
Cape Horn and the South Shetland Islands illustrates how direct 
wind impact and hydraulic forces may act in the same direction 
to give a compound current; for the winds of this region, which 
drive the water eastward through the strait, also pile water up 
against the coasts of Chile and the South Shetlands, whence the 
escape for the hydraulic current is also eastward through the 
strait 93 . 

Temporary Currents. — In addition to the more or less per- 
manent wind currents referred to above, there are temporary 
currents of considerable local importance which result whenever 
strong winds blow several days in a given direction. In the shal- 
low zone along a coast the entire mass of water may have so 
strong a " set " in the direction determined by the wind that one can 
readily note longshore transportation of bottom debris. If the wind 



126 CURRENT ACTION 

blows directly on shore, the temporary head may be sufficiently 
great to produce hydraulic currents of no mean importance. Thus 
during a furious gale on the 15th of January, 1818, the water 
in the Kattegat " rose 5| feet above the common waterstand " 94 . 
Northwest gales raise the level of the North Sea on the coast of 
Holland 4 or 5 feet above the normal tide heights, while an 
easterly wind raises the waters of the Black Sea against the coast 
of Bulgaria two feet above the ordinary level. Mitchell 95 esti- 
mated that a northeast storm blowing the shallow water of 
Long Island Sound westward toward Hell Gate in New York 
Harbor caused a rise of 6 feet at the latter point, and of 4 feet 
on the open coast. During the severe storm of November 21, 
1900, when the wind attained a velocity of 80 miles per hour at 
Buffalo, the lake level was raised 8.4 feet 96 . On the Zuyder Zee, 
with heavy west winds the water is lowered 8 feet on the west 
coast, and raised correspondingly with east winds. Owing to a 
heavy gale from the northeast in December, 1904, the water in 
the southern part of the Baltic Sea was raised from 8 to 12 feet 
above its normal level 97 . In the Galveston storm of September 
8, 1900, the Gulf waters rose 20 feet and were the principal 
agent of destruction in the city. During the storm of October 
5, 1864, on the coast of India, the water was raised 24 feet at 
Calcutta 98 . Such inequalities of levels must give rise to hydraulic 
currents of greater or less importance depending upon the configura- 
tion of the shoreline. According to Harrington 99 hydraulic cur- 
rents on the Great Lakes, resulting from the disturbance of water 
levels by storm winds, attain a velocity as high as 240 miles a day. 
Seasonal Currents. — Intermediate between the permanent 
currents resulting from such winds as the trades, and the tem- 
porary currents due to local storm winds, are currents which 
prevail during one season or another because of seasonal variations 
in the winds. Seasonal variations of current direction must in turn 
result in seasonal variations in the direction of debris transporta- 
tion, and hence in the size, form, and position of beaches. Thus 
the beach on the southwest point of Baker Island, in the Pacific 
Ocean near the equator, migrates from one side of the point to the 
other with the seasonal change in the winds 100 . Seasonal currents 
consist of true wind currents and of hydraulic currents resulting 
from the piling up of the wind-driven water against the continents. 
We may form some idea of the probable importance of these 



WIND CURRENTS 127 

currents if we know the seasonal inequalities of water level along 
different coasts. Harris has summarized a number of cases, 
showing seasonal inequalities which measure from a few inches 
to several feet 101 . It appears from this summary that the north- 
erly winds of winter blowing across the Gulf of Mexico produce 
low water at Galveston in February, while the southerly summer 
winds produce high water in October, the difference in height 
due to this cause being 1.5 feet. In winter the northeast mon- 
soons blow the water away from the coasts of the northern In- 
dian Ocean, and the southwest monsoons of summer raise the 
level, the difference varying from 1.8 to 3.2 feet. The south- 
westerly winds which prevail at Panama during much of the 
year raise the water against the northern shores of the Gulf of 
Panama 2 feet higher than the level which exists when the north- 
easterly winds of February blow the water away from those 
shores. In general, it is noted that sealevel is highest at most 
tidal stations in summer or autumn, and lowest in winter or 
spring; and since winds tend to blow from the ocean toward the 
land in summer, and from the lands out to sea in winter, it ap- 
pears that the piling up of the waters against the lands in summer 
must be the principal cause of high water at that time, rather 
than an expansion of the oceanic waters due to high summer 
temperatures, which at most could scarcely raise the ocean level 
0.1 of a foot 102 . 

It is evident that such large seasonal inequalities of level as 
have been noted above must be accompanied by currents which 
vary in direction or intensity, or both, with changes of the seasons. 
In the Strait of Bab-el-Mandeb at the mouth of the Red Sea 
there is a southeasterly current during the summer, because the 
summer monsoons of the northern Indian Ocean blow the sur- 
face water out of the Gulf of Aden, making its level lower than 
that of the Red Sea. In winter the current in the strait flows 
northwest, because the winter monsoons raise the Gulf level, 
and because the Gulf waters are less saline and therefore less 
dense than those in the Red Sea. The currents in the Strait 
often have a velocity of 30 to 40 miles a day, and as high a 
figure as 2J knots per hour, or 66 sea-miles per day, has been 
recorded 103 . These seasonal variations of the surface currents 
interfere with the circulation due to differences of salinity which 
would otherwise cause a constantly inflowing current on the 



128 CURRENT ACTION 

surface and as constant an outflowing bottom current. As 
with other currents produced by the wind, the direction and 
intensity of the seasonal wind currents, and of their resulting 
hydraulic currents, depend on a number of factors, among which 
wind velocity, water depth and shore configuration are of highest 
importance. There is a summer current northward through 
Bering Strait because southerly summer winds raise the waters 
of the shallow northern part of Bering Sea above the level of 
the Arctic Ocean, and the form of the shores offers a northward 
escape through a narrow channel 104 . In this case the current is 
probably in part a true wind current, although largely hydraulic. 
It will generally be found that near a coast the direct wind cur- 
rents do not move in the precise direction of the wind, but are 
deflected by the trend of the shore which introduces more or less 
of the hydraulic element into the currents. 

Planetary Currents. — There exist in the principal ocean basins 
gigantic whirls or eddies which are commonly referred to col- 
lectively simply as " the ocean currents." The principal cause 
of these great movements of the oceanic waters is now known 
to be the planetary wind systems which blow over their surface, 
although earlier students assigned a more important place to 
differences in oceanic temperatures. It should be noted, how- 
ever, that while the planetary winds constitute the prime cause, 
and we may therefore appropriately call the currents " planetary 
currents," many other factors must be recognized in any full 
explanation of their origin. Taking the North Atlantic cir- 
culation as an example, we find the southern side of the great 
whirl driven westward by the trade winds, and the northern 
side driven eastward by the prevailing westerlies. But account 
must also be taken of the deflective effect of obstructing land 
masses; of the constantly operating force arising from the 
earth's rotation which tends to deflect currents toward the right 
in the northern hemisphere; of the hydraulic action resulting 
when the waters driven westward are piled- up against the Carib- 
bean and Gulf coasts; of the large amount of rain and river 
water added to the ocean in the Gulf region; and, if we follow 
Ekman 105 and Carpenter 106 , of the water drawn into the Gulf by 
reaction currents (see below), and of the sinking cold water near 
the poles and rising warm water in low latitudes. It is simpler 
to treat currents of such complex origin in connection with the 



PLANETARY CURRENTS 129 

individual elements which combine to form them; but the 
planetary currents are sufficiently distinct and well known to 
require brief mention as such. 

Planetary currents may have a fairly high velocity under 
favorable conditions, as has already been noted for that part 
of the North Atlantic circulation called the Gulf Stream. In 
Florida Strait this current may reach a velocity of 4 miles an 
hour, which is sufficient to move large stones; and the current 
in the Strait of Yucatan has an even greater velocity. Such 
velocities are exceptional, however, and the bottom waters of 
even these currents move more slowly. Furthermore, planetary 
currents are usually located in deeper water far from the coast, 
and can therefore have little effect upon the shoreline. The 
swift current of the Gulf Stream in Florida Strait is some miles 
off shore and is separated from the land by another and slower 
current moving in the opposite direction. As Krummel 107 has 
pointed out, even where currents of this type do come in direct 
contact with the land they are almost always completely over- 
powered by tidal or other currents of much greater importance 
in shoreline processes. 

A good account of the former exaggerated ideas regarding 
the geological work of ocean currents will be found in Ruhl's 
review of the literature relating to the " Morphologischen 
Wirksamkeit der Meerestromungen ,U08 . While Ruhl does not 
discriminate sufficiently between the different types of currents 
found in the ocean, it is evident that many of the reports to 
which he refers deal with planetary currents. Pechuel-Loesche 109 
gives an interesting discussion of the conditions which render 
planetary currents unimportant agents on shoreline develop- 
ment, but tends to underestimate the transporting power of 
currents, and apparently does not distinguish sufficiently between 
the less important planetary currents and the movements due 
to tides and other forces which often have a very high degree of 
importance. Those tempted to ascribe shore forms to currents 
represented on charts or described in coast survey publications 
will do well to remember that currents so reported are usually 
studied several miles from shore where the water is deep enough 
to be important for navigation; whereas the shallow waters 
near the shore, of the highest importance to students of shore 
forms, are usually very imperfectly examined, if at all. The 



130 CURRENT ACTION 

fact that a certain current is observed several miles off a coast 
is no indication whatever that the waters near the shore move in 
the same direction. In shallow water, it is true, a planetary cur- 
rent may reach and scour the bottom; and it has been stated 
that such action is taking place under the Gulf Stream between 
Florida and Cuba, and on Blake Plateau southeast of Georgia 110 . 
Indirectly, these currents aid wave erosion by helping to distrib- 
ute the finer waste of the lands far over the ocean floor in water 
so deep that it cannot readily be returned to the shore zone 111 . 

Pressure Currents. — The weight of the atmosphere on the 
surface of the ocean is about 15 lbs. to the square inch, or about 
8| tons per square yard. It is evident that if atmospheric 
movements remove part of this weight in one place and increase 
it in another, the sea surface must rise where the pressure is par- 
tially relieved and sink where it is increased. Lubbock has 
shown that as a rule a rise of 1 inch in the barometer causes a 
depression in the height of high water amounting to 7 inches at 
London, and 11 inches at Liverpool 112 , while Bunt has found that 
a similar barometric rise produces a depression of 13.3 inches 
in the tides at Bristol 113 . Since these differences of level are 
usually distributed over broad areas, under the continuous ap- 
plication of pressures which alter but gradually, they probably 
do not often cause currents strong enough to be perceived. But 
if two water bodies connected by a strait are subjected to unequal 
pressure, currents may be produced in the strait which have a 
fairly high velocity. Ekman has shown that if the barometer 
fall 30 millimeters over the Baltic, the result would be the same 
as if the water in the Kattegat had risen 4 centimeters. This 
would be sufficient under certain conditions to reverse the sur- 
face stream normally flowing out through the connecting strait, 
and to give a distinct current into the Baltic 114 . In the Gulf of 
St. Lawrence a difference in atmospheric pressure is said to 
produce a flow of water from the area of higher to that of lower 
pressure, and to produce currents through the inlets connecting 
the Gulf with the ocean. High pressure over the Gulf of Mexico 
when there is low pressure over the ocean outside appreciably 
increases the velocity of the Gulf Stream 115 . It is difficult in 
these cases to make sure that the effects noted are wholly due 
to differences in pressure and are not affected to some extent 
by winds blowing from areas of high toward areas of low pressure. 



SALINITY CURRENTS 131 

Marked differences of pressure, so distributed over water bodies 
of the proper form and arrangement as to favor the production 
of pressure currents, do not appear to be sufficiently frequent 
or sufficiently lasting to make these currents of more than local 
and temporary importance. 

Convection Currents. — The warming of sea water causes 
it to expand and become lighter, while cooling causes greater 
density and hence increased weight. Therefore, if one portion 
of the ocean is warmed or cooled more than another, convection 
currents might be produced which would endeavor to restore 
a condition of perfect equilibrium. The planetary currents, as 
already noted, have been seriously regarded by some as mainly 
the result of unequal heating of the ocean. There is little 
doubt that a slow exchange of polar and equatorial waters is 
favored by temperature differences, the cold polar waters sink- 
ing and creeping equatorward in depth, while the warmed equa- 
torial waters flow poleward over the surface. That portion 
of this motion due to temperature conditions is, however, 
extremely slow. Marked differences of temperature at sealevel 
exist only between regions widely separated; and the resulting 
differences in ocean level are very small, since the greatest 
difference of specific gravity that can arise in the ocean from 
differences of temperature is about as 1 :1.0043 116 . Hence the con- 
vection currents which arise must be very feeble. It should be 
noted, furthermore, that the heat which tends to make sea water 
lighter by expanding it, also causes evaporation and thereby tends 
to increase the water's density. The effects of increased tempera- 
ture may often be more than counterbalanced by the effects of 
evaporation. It is doubtful whether, even in the case of a 
strait connecting two bodies of water, the currents arising from 
temperature differences alone are ever sufficiently strong to be 
of importance in shoreline processes. 

Salinity Currents. — The specific gravities of fresh water and 
sea water are very different, the relation at 15° C. being as 
1:1.027, and at 0° C. as 1:1.0283, if the sea water contains 3§ per 
cent of salt 117 . It follows that anything which locally dilutes 
the sea water, or which locally increases its salinity, will produce 
currents which may have a very high velocity. The most 
important causes of dilution or increase in salinity of the sea are 
rainfall, the outflow of river water, and evaporation. It is 



132 CURRENT ACTION 

evident that these processes must produce direct changes of 
level in addition to changes of specific gravity. Rainfall and 
the outflow of rivers raise the sealevel, while evaporation lowers 
it. Such differences of level must result in currents which will 
combine with the currents due to differences of specific gravity 
to form a single system of circulation, in which the higher, lighter 
water flows toward the lower and denser water on the surface, 
at the same time that the denser waters move along the bottom 
toward the region of water less dense. We will call the currents 
of this system, salinity currents. 

Rainfall is not equally distributed over the surface of the ocean. 
The equatorial rain belt has an excess of precipitation, and the 
same is true of higher latitudes where rains, snows, and melting 
ice contribute a large amount of fresh water to the sea. The 
two intermediate zones, from near the equator to about 40° 
north and south latitude, are characterized by deficient rainfall. 
There must be a tendency, therefore, for surface currents to 
move from both low and high latitudes toward the intervening 
areas of small precipitation. Such a movement in the open 
ocean would be comparatively slow, and must be largely masked 
by other currents of greater importance. 

Strongly marked differences in density are produced when ice 
melts in the sea, and the resulting currents should be well de- 
veloped in such regions as around the ice barrier of the Antarctic 
continent. Pettersson 118 and Sandstrom 119 have made special 
studies of such currents, and have shown that the melting ice 
dilutes the surface water and causes an out ward/ or seaward sur- 
face movement. The water below the ice is cooled, its density 
thereby increased, and it sinks to the bottom and flows outward 
as a bottom current. Between these two there must result an 
inward moving zone of water which has been neither cooled nor 
diluted. Pettersson goes so far as to attribute an important 
part of the main oceanic circulation to ice-melting, an extreme 
view not shared by most oceanographers. Barnes 120 has in- 
vestigated the value of ice-melting currents in enabling navi- 
gators to locate icebergs from a distance; but it has not yet 
appeared that currents of this origin are of importance in shore 
processes. 

Fresh water poured into the ocean by a large river raises the 
sealevel at that point and lowers the density of the ocean water. ' 



SALINITY CURRENTS 133 

Surface currents tend to move out in all directions, and the 
bottom, denser water to creep in toward the river mouth. On 
an open coast the surface currents may be strong in the immediate 
vicinity of the river's mouth but at greater distances the move- 
ments must be relatively feeble. Where rivers empty into a 
gulf or bay the level may be so much raised as to cause a very 
strong current at the outlet to the ocean. The unusual strength 
of the Gulf Stream may in part be due to the large amount of 
water brought into the Gulf of Mexico by the Mississippi and 
other rivers. Even if the fresh water does not actually raise 
the level of the Gulf, it must prevent a lowering of that level by 
evaporation, and thus cause a virtual rise relatively to the ocean 
outside 121 . The surface currents moving from the Arctic Ocean 
through Denmark and Davis Straits into the Atlantic are prob- 
ably in part salinity currents. " The considerable precipitation, 
the influx from several large rivers, and especially the small 
evaporation, all go to maintaining a rather low density for 
Arctic waters as well as an increased, but of course very small, 
elevation of the surface. . . . Doubtless a considerable amount 
of water passes as an undercurrent from the Atlantic into the 
Arctic through the straits east and west of Iceland " 122 . In the 
Gulf of St. Lawrence the waters have a lower density and higher 
surface than *in the Atlantic, and a surface current of 2 knots 
per hour through Cabot Strait is attributed by Harris, in part 
at least, to this fact 123 , although Dawson thinks the influence of 
the St. Lawrence River water upon currents in the Gulf is apt 
to be exaggerated 124 . 

Salinity Currents at the Mouth of the Baltic Sea. — The enor- 
mous influx of river water into the Baltic Sea causes that water 
body to be almost fresh at its northern end, and to have a 
low density throughout; while its surface is generally believed 
to be higher than the mean level of the sea outside. On 
this basis we should expect a surface current passing outward 
through the straits at the mouth of the Baltic, and an under- 
current of heavier, salt water flowing into the Baltic along the 
bottom. Such a circulation exists, and the velocity of the 
outflowing surface stream is usually given as 1 to 2 knots per 
hour in the Kattegat, but may be double this along the Nor- 
wegian coast of the Skagerack. It is strongest in spring and 
early summer, when the influx of fresh water into the Baltic 



134 CURRENT ACTION 

is at its maximum 125 . As Otto 126 has pointed out, unless prevented 
by other currents of greater power, such a circulation would re- 
sult in the shore debris's being controlled by the outward flowing 
surface current, while the bottom debris in deeper water would 
be swept in the opposite direction by the inflowing bottom cur- 
rent. Ekman 127 attributes the deep channel in the Skagerack 
and Kattegat to the scouring action of the bottom current, which 
prevented deposition along its course of the sediment now 
covering the bottom of the North Sea; but he thinks, apparently 
without sufficient reason, that this was done when the land 
was higher and melting ice supplied larger volumes of outflowing 
waters. Perhaps a more probable interpretation is that the 
channel represents a normal river valley, submerged, and since 
kept open by current action. 

Pettersson 128 has questioned the existence of a higher surface 
level in the Baltic on the ground that accurate measurements 
show the water level at Ystad and Landsort on the Baltic coast 
to be .024 and .023 meters respectively below the mean annual 
level at Varberg on the shore of the Kattegat; while Bjerknes 
and Sandstrom 129 contend that the difference in density between 
the Baltic water and that outside is not sufficient to account 
for the existing currents in the Belts and Kattegat. It should 
be noted, however, that the currents behave in a manner normal 
for salinity currents, and they are generally interpreted as such. 
The Black Sea receives every year 152 cubic kilometers (about 
36 cubic miles) more fresh water than escapes by evaporation. 
Strong salinity currents therefore exist in the Bosphorus, the 
outflowing fresher surface stream at Constantinople having a 
velocity of 123 centimeters per second, or over 2 knots per hour. 
At a depth of 25 meters the heavier salt water is flowing inward 
with a velocity of 73 centimeters per second, the velocity de- 
creasing slowly with increase in depth 130 . 

Salinity Currents at the Strait of Gibraltar. — Evaporation is 
an effective agent in producing salinity currents but in this 
case the surface current must of course flow inward toward 
the region of evaporation, where the water is increasing in den- 
sity and the surface is being lowered; while the heavier salt 
water will flew outward at a lower level. A striking example 
of such circulation is found in the Strait of Gibraltar. The 
annual evaporation from the surface of the Mediterranean 



SALINITY CURRENTS 135 

amounts to a layer of water at least 3 meters deep according to 
Fischer 131 , and greatly exceeds the influx of fresh water, with the 
result that the waters in the sea become denser and the surface 
lower than is the case in the Atlantic Ocean. The higher and 
lighter waters of the Atlantic flow into the Mediterranean as a 
surface stream of marked strength, while deep-water obser- 
vations prove that a strong current of more saline water moves 
outward on the bottom. The great velocity of these currents is 
a matter of considerable interest. Maury 132 quotes the following 
from the abstract log of Lieutenant W. G. Temple for March 
8, 1855, relating to the inflowing surface current: " Weather 
fine; made 1| pt. leeway. At noon, stood in to Almiria Bay, and 
anchored off the village of Roguetas. Found a great number 
of vessels waiting for a chance to get to the westward, and learned 
from them that at least a thousand sail are weatherbound be- 
tween this and Gibraltar. Some of them have been so for six 
weeks, and have even got as far as Malaga, only to be swept 
back by the current. Indeed, no vessel had been able to get 
out into the Atlantic for three months past." It would seem 
from this that the surface salinity current, reinforced no doubt 
by an hydraulic current due to heaping up of water in the Gulf 
of Cadiz under westerly winds 133 , and perhaps also to some ex- 
tent by a direct wind current, had a velocity sufficiently great 
to prevent sailing vessels from passing westward to the Atlantic 
for months at a time. Helland-Hansen 134 has shown that tidal 
currents also affect the movement of the waters in the strait, 
the direction of flow at a depth of 10 meters even being reversed 
from its usual inward course for a brief period on the day of his 
observations. The maximum velocity of the inflowing current 
at a depth of 10 meters was on that day, 118 centimeters per 
second, or 2.3 knots per hour. On another day the velocity of 
the inflowing current at a depth of 5 meters was 150 centimeters 
per second, or nearly 3 knots per hour. At a depth of 46 meters 
the inflowing current had a velocity of 1.8 knots, and at a depth 
of 91 meters a velocity of 2 knots. The depth for the next series 
of observations was 183 meters (100 fathoms) and both here and 
below the current was continuously flowing out into the Atlantic. 
On the surface the current nearly always flows inward with a 
velocity of about 3 knots per hour 135 . 

The strength of the outflowing bottom current is more re- 



136 CURRENT ACTION 

markable than that of the inflowing surface current. With 
274 meters (150 fathoms) of wire out the exact depth could not 
be learned because the wire was so strongly bowed by the force 
of the current. A maximum velocity of 227 centimeters per 
second, or 4.4 knots per hour, was recorded. When sent down 
with 366 meters of wire the apparatus was wrecked, apparently 
by being bumped against stones on the bottom 136 . Sir James 
Anderson has stated that the velocity of this outflow is so great 
at the bottom that at a depth of 500 fathoms the wire of the 
Falmouth cable near Gibraltar was ground like the edge of a 
razor, so that it had to be abandoned and a new one laid well 
inshore 137 . Captain Nares reports that he could get no specimen 
of the bottom, probably because of a " perfect swirl at that 
depth " 138 . Such currents must be very effective, not only in 
scouring the bottom at great depths, but also in transporting 
to a final resting place in very deep water any debris which may 
be delivered to it by the agitated surface waters. 

Salinity Currents at the Strait of Bab-el- Mandeb. — Important 
salinity currents due to evaporation occur in the Strait of 
Bab-el-Mandeb at the mouth of the Red Sea. This sea is 
located in one of the dryest regions of the world, and possesses 
the highest mean annual salinity of any body of water in com- 
munication with the open ocean 139 . As a consequence there 
is an inflow of lighter water on the surface of the strait and an 
outflow of heavy salt water on the bottom, except when this 
circulation is interfered with by hydraulic currents caused by 
the monsoon winds. The velocity of the inflowing current 
is variously stated as from 30 to 65 knots per day, or a maxi- 
mum of about 2 j knots per hour 140 . The outflowing bot- 
tom current varies from 1 to 3 knots per hour. Even the lowest 
velocity mentioned for either stream is sufficient to move fine 
gravel; and it cannot be doubted that currents of this type 
play an important role along the shores of straits and the narrow 
parts of adjacent seas, even though the swiftest current is never 
found in the immediate vicinity of the shoreline. 

River Currents. — Rivers entering the sea have their currents 
checked before they have advanced far into the quieter water, 
and in place of a narrow stream of fresh water moving forward 
under the impetus of the river's original velocity, there are de- 
veloped slower hydraulic currents due to the piling up of the 



RIVER CURRENTS 137 

waters, salinity currents due to differences in specific gravity, 
and reaction and eddy currents generated by the dynamic force 
of the original stream. For a short distance, however, one may 
recognize the true river current, the extent of its penetration as 
such into the sea depending on the volume and velocity of the 
river, the form of the shore and sea-bottom, and other factors. 
Dall 141 has attributed the clockwise circulation of the Bering Sea 
in part to river currents which enter the eastern side of the sea 
with a southwestward trend. 

As the river current is checked by contact with the quieter 
waters of the sea it must of course deposit the debris it is trans- 
porting, the coarsest first, the finer as the current grows more and 
more sluggish. If the river is heavily laden with sediment, and 
the water body into which it empties is not greatly agitated 
by other types of currents, much of the debris will remain where 
first dropped to form a delta. Most rapid deposition occurs 
beneath and along the immediate margins of the river current, 
with the result that the current is ultimately confined between 
walls of its own deposits and prevented from coming in contact 
with the adjacent waters until it has passed beyond the limits 
of the embankments. Thus, the river current is carried farther 
and farther out into the oceanic waters between the two sides of 
an elongating delta lobe, as in the case of the Mississippi delta, 
some lobes of which have advanced into the Gulf of Mexico at 
the rate of from one hundred to several hundred feet a year. 
On the other hand, if a strong current of any type sweeps along 
the coast opposite the mouth of a river, the river current may be 
deflected so as to merge with the longshore current. As the river 
current gradually loses its identity the sediment is carried on 
by the higher velocity of the more powerful longshore current. 
Under these conditions no delta will form. Assuming that a 
river brings down a significant amount of sediment, its ability 
to form a delta does not depend upon its entering a tideless sea, 
as is usually stated, but rather upon its entering a comparatively 
currentless sea. The Indus builds its delta in a sea having a 
tidal range of 10 feet, while the Ganges delta has formed where 
the range is 16 feet. The theory that deltas are restricted to 
tideless seas is fallacious. If the river current is stronger than 
other currents in the sea at the point of its embouchure, and in 
consequence is carrying debris which those other currents can- 



138 CURRENT ACTION 

not transport, a delta will form, whatever may be the tidal range. 
If the strength of any other type of current exceed that of the 
river current at the point of embouchure, no delta will form. 

It often happens that the river current is strongest at the 
immediate point of embouchure to begin with, although a more 
powerful current sweeps along the coast some distance out in 
the sea. This is especially apt to be the case where a river enters 
the sea at the head of a reentrant angle or bay. Delta formation 
will then proceed until the river current has been carried seaward, 
by the advancing delta lobe, to the point where it conflicts with 
and is overcome by the longshore current. Such seems to have 
been the history of the Nile delta; for although the river cur- 
rent brings out to sea 36,600,000 cubic meters of silt annually, 
this vast tribute of sediment does not add to the seaward extent 
of the delta, because " a powerful marine current sweeps past the 
coast and carries the sediment eastward beyond the most easterly 
mouth of the river " 142 . Much of the sediment now brought 
down by the Amazon is carried seaward with the aid of strong 
tidal currents, then caught up by the Northern branch of the 
South Equatorial current, which transports part of it over 300 
miles to deposit it along the coast of Guiana 143 . The forms of 
deltas will evidently depend not only upon the original form of 
the shoreline, the nature and quantity of the debris brought 
down by the river, and the manner in which the river shifts its 
position upon the delta; but also upon the extent of wave action, 
and the direction and strength of coastal currents of different 
types as compared with the strength and direction of the river 
current. 

Reaction Currents. — F. L. Ekman 144 has shown that since a 
river flowing into the sea sets adjacent water particles moving 
forward in the same direction, thereby increasing the volume of 
the current more rapidly than its velocity is decreased, there 
must be an influx of seawater toward the mouth of the river to 
make good the resulting deficiency. " Every river or brook 
which falls into the sea gives rise to an undercurrent directed 
toward its embouchure. These undercurrents are so distinct 
and the causes that produce them so active, that in calm weather 
their presence may be easily observed at the mouth of the most 
insignificant rivulet that falls out over the surface of the sea." 
To such currents Ekman gives the name " reaction streams." 



EDDY CURRENTS 139 

Cornish has called them " induction currents " 145 . Investigations 
of the outlet of the Gota-Elf into the Kattegat showed that a 
reaction current flowed well into the bed of the river as a dis- 
tinct bottom current of salt water. A sunken object was moved 
up the river channel by this current; in direct opposition to the 
surface flow 146 . It was shown that this current could not be 
explained as a mere salinity current due to differences of specific 
gravity between the fresh and salt water. Ekman even goes 
further, and regards the bottom currents at the outlet of the 
Baltic Sea and in the Strait of Gibraltar as in large part reaction 
currents. Cronander 147 ; on the other hand, would seem to doubt 
the existence of true reaction currents, even at the outlet of 
the Gota-Elf where Ekman made his principal study. While 
there are probably reaction currents developed both at the 
mouth of the Baltic and at the inlet to the Mediterranean, Ek- 
man seems to push his theory too far and to lose sight of the 
facts that salinity currents of large volume must exist under the 
conditions obtaining at such straits as those in question, and that 
any reaction currents found there are secondary phenomena of 
less importance than the currents which give rise to them. 
Reaction currents have been further studied by V. W. Ekman, 
the son of the investigator quoted above, and some of his con- 
clusions are embodied in a valuable paper 148 published in 1899. 
According to his studies, reaction currents are not always well 
developed at the mouths of rivers, and may even fail entirely 149 . 
On the other hand, Buchanan 150 goes so far as to explain the sub- 
marine gorge opposite the mouth of the Congo as due to reaction 
currents, which prevented sedimentation in the seaward prolonga- 
tion of the river's course while the continental shelf on either side 
was being built up. 

There can be little doubt that reaction currents must have 
some effect upon the transportation of debris in the vicinity of 
river mouths, and possibly in other localities. But while bot- 
tom debris has been observed in motion under the influence of 
these currents, our knowledge of their geological work and its 
relative importance is very slight. 

Eddy Currents. — Closely related to the reaction currents 
described above are the eddy currents, which also result from 
the dynamic force exerted by the moving waters of currents 
of other types. In the typical reaction current the water moves 



140 



CURRENT ACTION 



in under the original current which produced it. Eddy cur- 
rents (called " draught currents" by Bache), on the other hand, 
are surface whirls in which the water next the original current 
moves forward beside it, the opposite side of the whirl flowing 
in the reverse direction. Thus the clockwise planetary whirls 
of the northern oceans give rise to counter-clockwise eddies 
on their outer sides. The surface manifestations of these whirls 
are so well known that it seems desirable, notwithstanding their 
close affinity with the reaction currents, to treat them separately 
under the name of eddy currents. 




Fig. 21. — Eddy currents in the Gulf of Honduras and Mosquito Gulf. 

The salinity current entering the Mediterranean Sea moves 
eastward along the northern coast of Africa, aided by the prevail- 
ing westerly winds. In the gulf off the coast of Tripoli it causas 
a well marked eddy current. The Equatorial Current flowing 
through the Caribbean Sea produces one eddy current in the 
Gulf of Honduras and another in the larger embayment of 
Mosquito Gulf north of Panama (Fig. 21). Tidal currents enter- 
ing New York Harbor cause an eddy current just inside of Sandy 
Hook which must affect the development of that spit 151 . Gul- 
liver has shown that eddy currents developed by tidal currents 
in estuaries may help to determine the detailed form of the 
shoreline 152 , and Abbe has even attributed the formation of the 



COMPLEXITIES OF CURRENT ACTION 141 

great Carolina capes to eddy currents generated by the Gulf 
Stream 153 . A great deal of importance has been attributed 
the Florida counter-current in determining the shore forms 
to along the eastern and southern coasts of that peninsula 154 . 
While there may be some question as to the origin of this cur- 
rent, and some even doubt whether its existence has been fully 
established, Perkins 155 is of the opinion that in so far as it is a 
reality it is probably an eddy current generated by the Gulf 
Stream. 

Deflection of Currents, — All of the currents above described 
are subject to the deflective effect of the earth's rotation. Those 
in the northern hemisphere are deflected to the right, those in 
the southern hemisphere to the left. The deflection is un- 
recognizable in short, temporary currents, such as those arising 
from wave action; but is prominently shown by large con- 
tinuously moving currents, like those of the planetary circulation, 
and may even be observed in the smaller salinity currents and 
other similarly restricted circulations. 

COMPLEXITIES OF CURRENT ACTION 

The preceding discussion of the several types of currents 
encountered in the sea is sufficient to show that the subject is by 
no means a simple one. We have endeavored to analyze the 
origin and nature of each type separately, and to gain some idea 
of its probable relative importance. But we fully realize that 
in nature one seldom encounters one of these currents operating 
alone. In almost every case the ocean water moves in a given 
direction because of the combined influence of several forces. 
At the Strait of Gibraltar the inward surface flow may at a given 
moment represent the combined effect of salinity, wind, hydraulic, 
tidal, pressure, and reaction currents, all moving in the same 
direction. Off Storeggen movements of the water toward the 
northeast were found to result from the combined action of 
planetary and tidal currents 156 . Along the south coast of Alaska 
a prominent planetary or eddy current and the local tidal currents 
are so far affected by wind currents that it has been asserted that 
" the currents along this part of the coast are controlled entirely 
by the winds " 157 . The currents in the Strait of Bab-el-Mandeb 
are variable in character because salinity, wind, and hydraulic 



142 CURRENT ACTION 

currents combine in varying proportions at different times of 
the year; and they are further " confused through the irregular 
tidal influence felt there " 158 . Tidal currents on the south coast 
of Cantyre are uncertain and imperfectly understood, being 
much affected by wind currents 159 . Ekman has described the 
complex nature of the Gulf Stream 160 ; Buchan and Ekman have 
both discussed at length the combined effects of salinity and 
temperature on oceanic circulation 161 ; and Parsons has described 
the combination of tidal and hydraulic currents in New York 
Harbor, and mentioned the difficulties arising from the interfering 
action of salinity, wind, and eddy currents 162 . Wind, pressure, 
and hydraulic currents may combine to reverse the normal 
outflowing salinity current at the mouth of the Baltic 163 , while 
the similar current out of the Black Sea is reversed during strong 
south winds 164 . Cronander even goes so far as to reject the com- 
monly accepted theory of salinity currents at the mouth of the 
Baltic, and regards both surface and bottom currents as due to 
the wind 165 . The continuous outflowing current just inside the 
northern end of Sandy Hook is part of the time a true tidal 
ebb current, and part of the time an eddy current developed by 
the flood tide 166 . Otto has shown the difficulty of analyzing the 
movement of shore and bottom debris by currents along the 
south shore of the Baltic 167 . 

Further complication arises from the fact that along the same 
shore different types of currents may act with very different 
strengths, and the same current may have very different power 
in two adjacent areas. In the shallow water close to the beach, 
wind and wave currents are extremely effective, while tidal 
currents may be scarcely perceptible. A few yards out from 
the same shore, in water of moderate depth, a tidal current may 
sweep with irresistible force, while the wave current will be too 
feeble on the bottom to move coarse debris. Divers have found 
that while large surface waves will not interfere with their work 
on the bottom, a tidal current may sweep so strongly over the 
same spot that it becomes impossible to stand against it 168 . 
Let us imagine that in such a case the wind current and beach 
drift is toward the east, while the tidal current runs toward the 
west. At the shore one observer notes that throughout the 
year the wind and waves invariably cause the shingle to be 
moved visibly eastward. Another observer finds that the only 



COMPLEXITIES OF CURRENT ACTION 143 

known source of supply for the rocks from which the shingle is 
derived lies to the east, and hence concludes that tidal currents 
transport the material westward. Both are right, for the tidal 
current carries the shingle westward so long as it remains in 
deep water; but as fast as part of the material is moved into 
shallow water, or is thrown upon the beach by unusually large 
storm waves, it comes under the influence of the eastward di- 
rected forces; and it continues to move in this direction so long 
as it is not washed back into deeper water where the westward 
moving tidal current prevails. 

Conflicting Opinions Regarding Current Action. — A brief ex- 
amination of the literature is sufficient to show that in cases 
similar to the one supposed above, one observer has frequently 
denied the validity of another's interpretation at the same time 
that he maintained the correctness of his own. The engineers 
and other authorities in Great Britain have of necessity paid 
much attention to the problems of coast erosion and transporta- 
tion; and if one looks through some of the papers on this subject 
published in " Minutes of Proceedings of the Institution of Civil 
Engineers," he will be surprised at the wide differences of 
opinion there expressed by different experts, on the question as 
to what agent effects the longshore transportation of sand and 
shingle. Discussions on this point cover many pages and some- 
times required the entire time of two or more meetings for their 
consideration. According to the views expressed, both in these 
discussions and before other learned societies, the transportation 
of shingle is due " chiefly, if not entirely, to the action of wind 
waves" (J. Scott Russell); " to the effects of the ocean-wave or 
ground-swell" (J. N. Douglas), since " waves possessed sufficient 
power to move shingle at considerable depths " (Joshua Wilson), 
or even " at very great depths" (E. Belcher); whereas "Very 
little was ascribable to action of the tide " (G. B. Airy), for " the 
tide current does not affect the depths of more than 12 or 14 
feet" (E. Belcher), and "the tidal streams had not sufficient 
velocity to exercise any mechanical power whatever " (R. A. C. 
Austen). On the other hand, we have the opinions that "shingle 
could scarcely be moved by the heaviest waves at greater depth 
than three fathoms " (J. M. Rendel) ; the formation of the great 
shingle deposit of the Dungeness " should be attributed, princi- 
pally, to the counter-current of the tides " (G. Rennie); and "at 



144 CURRENT ACTION 

Cahore the driftage is solely due to the flow-tide currents " 
(G. H. Kinahan), while the movement of another shingle beach 
was due to " submarine currents which had the power of carry- 
ing pebbles along the shore at great depths" (Joseph Gibbs). 
As Hunt 169 has pointed out, although " the action of waves on 
sea-beaches and sea-bottoms has been much discussed during the 
last fifty years, . . . there is scarcely an important point con- 
nected with the subject that is accepted without dispute, whilst 
not only the opinions, but even the recorded observations of 
skilled observers are often, to all appearance, in hopeless conflict.' ' 

Not only the cause of shingle transportation, but also such 
questions as whether large or small debris travels farthest, and 
under what conditions waves build up or destroy shingle beaches, 
are in dispute. According to Coode 170 large pebbles travel far- 
thest because they move more readily than small ones ; Redman 171 
agrees to the greater travelling power of the large material, as 
does also Reade 172 , who rejects Coode's explanation, however, 
and suggests one of his own. On the other hand Prestwich 173 , 
Palmer 174 , Airy 175 , Spratt 176 , and Geikie 177 hold that the smaller 
pebbles are those which travel farthest. 

The question as to whether the shingle travels east or west on 
the great Chesil Bank of the south coast of England has long 
been disputed, with eminent authorities on both sides. Whether 
the largest or smallest pebbles tend to accumulate at the top of 
the beach has likewise been vigorously debated. Coode 178 , Mat- 
thews 179 , and Shield 180 state that with offshore winds the waves 
build up shingle beaches, while with onshore winds the beaches 
are cut away; but Kinahan 181 is of the opinion that the reverse is 
the case. Palmer 182 concluded that when more than ten breakers 
arrived in a minute the beach was eroded, when less than ten, 
the beach was built up; but Coode 183 declares that so far as a 
rule can be established it is that any number of breakers greater 
than nine per minute causes the building up of the beach, while 
seven or less produces erosion. 

Reasons for Conflicting Opinions. — The remarkable disagree- 
ment which has been illustrated above is not so surprising when 
one considers the complex origin of currents in the sea, and the 
enormous variability of wave and tidal action along a coast. 
There can be no doubt that in some localities tidal currents play 
a more important role in the longshore transportation of sand 



COMPLEXITIES OF CURRENT ACTION 145 

and shingle than do wave currents, beach drifting, and related 
forces; and it is equally certain that in many other localities 
the currents associated with wave action are more important 
transporting agents than are those of tidal origin. In still other 
localities it may be difficult to determine which of these two 
types of currents exercise a predominant influence upon the 
shoreline, or whether some other current may not be more 
important than either. The present writer entertains no doubt 
that as a whole waves are far more important agents of long- 
shore movement of beach material than are tides or other forces. 
It does not appear that the conclusions of the authorities 
quoted above where based on any adequate analysis of the 
complex forces operating along the shore. On the contrary, in 
a large number of the instances cited conclusions were based on 
isolated observations in a limited number of places, and while 
these observations were usually made with skill and accuracy, 
they were utterly inadequate as a basis for general conclusions 
concerning such difficult problems as those encountered at the 
shoreline. Erroneous ideas as to the strength of certain cur- 
rents have crept into standard textbooks, as for example Reade's 
conclusions regarding the strength of tidal currents near Gibraltar 
based on observations which really related to salinity currents 184 . 
This is inevitable, in view of the limited knowledge of ocean 
currents which exists even to the present time. Again, the 
resemblance between certain currents of different origin is so 
close that special care must be taken properly to distinguish 
them. Thus, at the mouth of a river we may have a landward 
directed bottom current which may be a salinity current, a 
reaction current, or a floodtide current, or all of these combined. 
Mitchell 185 describes such a landward current at the mouth of the 
Hudson River, and regards it as a true flood-tide current which 
creeps in along the bottom because it is heavier than the brack- 
ish water in the river. Harris 186 refers to this same current as one 
of the " counter currents at the bottom of the channel " caused 
by " a fresh-water stream discharging into the ocean," and refers 
to Mitchell's work apparently under the impression that Mit- 
chell regarded the movement as a reaction current. It seems to 
the present writer that the conditions in this water body are 
distinctly unfavorable for the development of either salinity or 
reaction currents of large volume and appreciable velocity, and 



146 CURRENT ACTION 

that Mitchell's work demonstrated the tidal origin of the prin- 
cipal movement. The fact that a certain current flows landward 
along the bottom of a river channel and consists of heavier, more 
saline water than is found above it, does not mean that such 
current is caused by either the dynamic force of the river current 
or the difference in specific gravity between salt and fresh water. 

Another source of difficulty in interpreting current movements 
arises from the fact that the currents usually observed are not 
always the ones which do the most work. Thus, the prevailing 
winds may cause almost continuous but weak wind currents 
and wave currents in one direction, whereas the greatest storms 
may cause short-lived but remarkably vigorous wind and wave 
currents in the reverse direction. More material may be moved, 
and moved a greater distance, by the latter currents than by 
the more continuous weaker ones. Hence, the direction for the 
dominant transportation of beach material is contrary to the 
prevailing currents. It has happened that in such a case one 
observer erroneously concluded that wave and wind currents had 
nothing to do with the distribution of the beach material; while 
another assumed that the material must move with these pre- 
vailing currents, and accordingly developed erroneous theories 
regarding the laws of shingle transportation. 

A further cause of misunderstanding is the long time which 
waves and currents have taken to produce certain effects ob- 
served along the coast. To the geologist, who is familiar with the 
slow operation of the forces of nature, it seems that waves, at 
least, work with comparative rapidity. But the ordinary ob- 
server, and even the skilled engineer, may find it difficult to 
attribute the vast accumulations of sand and shingle on our 
coasts to forces which seem to him almost impotent in comparison 
with the great work accomplished. Such is the view repeatedly 
expressed by Wheeler in his volume on " The Seacoast." In 
the opinion of this eminent engineer, " a careful consideration 
of all the circumstances that attach to beaches can only lead to 
the conclusion that the results which have been attained must 
be due to other and mightier forces than those now in existence." 
"It is certain that the enormous mass of sand, which now covers 
the littoral of the sea and the beds of estuaries, cannot have 
been deposited by existing agencies." " The enormous accumu- 
lation of shingle known as the Chesil Bank . . . must have been 



COMPLEXITIES OF CURRENT ACTION 147 

accomplished under conditions very different to those which now 
exist" 187 . The geologist, on the other hand, recognizes in these 
extensive shore deposits the effects of ordinary forces of nature 
continued for a very long period of time. There is nothing in 
the deposits described by Wheeler to excite wonder, except their 
extent; and large deposits may be made by ordinary forces 
working a long time as well as by extraordinary forces working 
a short time. I have examined some of the largest beach ac- 
cumulations on the English and other European coasts, as well 
as those on the Atlantic coast of the United States ; and see no 
reason to doubt that they have been produced by the same waves 
and currents which are still at work upon them. 

Conclusions. — In the preceding paragraphs I have endeavored 
to give the reader some idea of the serious difficulties which con- 
front the student of shore processes. It must be confessed, 
however, that it is much easier to describe the complexities of 
currents, and to point out the mistakes which are frequently 
made in interpreting them, than it is to solve those complexities 
in a given case and present a discussion which is so conclusive as 
not to be open to criticism. Nevertheless, it was essential that 
we should enter upon our treatment of shoreline forms with a 
broad view of the problems connected with wave and current 
action, and with some appreciation of the variety of the forces 
which operate at the shore in different places and at different 
times. We are now prepared to consider the development of 
shorelines more intelligently, even if we are not prepared to 
assert with positive ness the precise part played by different cur- 
rents in shaping each portion of any given shore. 

The time will come when our present limited knowledge of 
both wave and current action will be enormously extended by 
means of improved mechanical appliances. The movements of 
debris upon the bottom at considerable depths during wave ac- 
tion, concerning which we can only theorize at present, will be 
actually observed by special electrical apparatus. Wave cur- 
rents and currents of other types will be studied by observing the 
exact movements of debris under their control. Limited areas 
of the coastal waters will be exhaustively studied, every detail 
of the currents analyzed with care under varying conditions, and 
the movements of debris determined with far greater precision 
than is now possible. While shoreline problems will never be 



148 CURRENT ACTION 

simple, the researches of the future will yield a body of facts 
which will enable the geologist and engineer of some coming 
generation to predict shore changes and plan harbor and coast 
defenses with an assurance which will contradict the assertion 
of the present maritime engineer, that the forces operating at 
the shore are among the forces of nature, " which are subject to 
no calculation." In the meantime we may take some satis- 
faction from the fact, which will presently appear, that a great 
deal may be learned about current action by studying the forms 
of beaches, since these often provide a more reliable indication 
of the dominant currents in a gi /en locality than do any direct 
observations feasible at the present time. 

RESUME 

We have reviewed the essential characteristics of the more 
important types of currents, and gained some idea of their rela- 
tive strength, and comparative importance in shore processes. 
It appears that a great variety of wave currents operate in a 
most complicated and irregular manner, sorting and transport- 
ing debris in shallow water and on the beach in different ways 
depending on differences in outline of shore, angle of offshore 
slope, angle of wave approach, size of waves, kind of waves, 
and other factors. Tidal currents are scarcely less complicated, 
although developed on a much larger scale, and therefore more 
easily studied. Seiche currents, wind currents, planetary cur- 
rents, pressure currents, convection currents, salinity currents, 
river currents, reaction currents, eddy currents, and hydraulic 
currents have all been considered ; and we have found that 
some of them have a small degree of local importance only, while 
others are of wide-spread occurrence, or have a volume and 
strength which make them of very great significance. These 
currents are deflected from their initial courses by the earth's 
rotation; they combine with each other or counteract each 
other in the most complicated ways; they are not infrequently 
wrongly identified, and their manner of working and relative 
importance are often matters of dispute. Some knowledge of 
their behavior is nevertheless essential to an understanding of 
shore forms, and we may in turn expect to gain further know- 
ledge of the currents themselves when we study the forms they 
have helped to produce. 



REFERENCES 149 



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152 CURRENT ACTION 

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67. Crosby, W. O. A Study of the Geology of the Charles River Estuary 

and Boston Harbor, with Special Reference to the Building of the 
Proposed Dam across the Tidal Portion of the River. Technology 
Quart. XVI, 88, Boston, 1903. 

68. Mitchell, Henry. The Under-run of the Hudson River. U. S. Coast 

Survey, Report for 1887, p. 305, 1889. 

69. Browne, W. R. The Relative Value of Tidal and Upland Waters in 

Maintaining Rivers, Estuaries, and Harbors. Min. Proc. Inst. Civ. 
Eng. LXVI, 20, 1881. 

70. Mitchell, Henry. The Harbor of New York: its Condition, May 

1873. U. S. Coast and Geodetic Survey, Rept. for 1871, p. 115, 
1874. 

71. Mitchell, Henry. On the Circulation of the Sea through New York 

Harbor. U. S. Coast Survey, Rept. for 1886, p. 411, 1887. 

72. Salisbury, R. D. Physiography, p. 736, New York, 1907. 

73. Branner, J. C. The Poror6ca, or Bore, of the Amazon. Science. IV, 

488-492, 1884. 



REFERENCES 153 

74. Cornish, Vaughan. On the Principles which Govern the Transporta- 

tion of Sand and Shingle by Tides and Waves, with a Note on the 
Severn Bore. Jour. Roy. Soc. of Arts. LX, 1123, 1912. 

75. Bache, A. D. On the Tidal Currents of New York Harbor near Sandy 

Hook. U. S. Coast Survey, Rept. for 1 858, p. 201, 1859. 

76. Harris, R. A. Manual of Tides. Part V. U. S. Coast Surv. Rept. 

for 1907. Appendix No. 6, p. 340, 1907. 

77. Cornish, Vaughan. On Sea Beaches and Sand Banks. Geog. Jour. 

XI, 531, London, 1898. 

78. Harris, R. A. Manual of Tides, Part V. U. S. Coast Surv. Rept. for 

1907. Appendix No. 6, pp. 340-377, 1907. 

79. Parsons, H. de B. Tidal Phenomena in the Harbor of New York. 

Proc. Am. Soc. Civ. Eng. XXXIX, 670, 1913. 

80. Thoulet, Jules. L'Ocean: ses Lois et ses Problemes, p. 332, Paris, 

1904. 
Krummel, Otto. Handbuch der Ozeanographie. II. Die Bewegungs- 
formen des Meeres, p 180, Stuttgart, 1911. 

81. Reclus, Elisee. The Ocean, p. 123, New York, 1873. 

H* 82. Anonymous. A Tidal Problem. Nature. XXI, 186, 1880. 

— 83. Cold, Conrad. Kiisten-Veranderungen im Archipel, p. 35, Marburg, 

1886. 

84. Lindenkohl, A. Oceanography. Encyclopedia Americana, 1904. 

85. Harrington, M. W. Surface Currents of the Great Lakes. Bull. B, 

U. S. Dept. Agriculture, Weather Bureau, 1895. 

86. Taylor, Frank B. Personal communication. 

— 87. Grabau, A. W. Principles of Stratigraphy, p. 243, New York, 1913. 
88. Hunt, A. R. On the Action of Waves on Sea Beaches and Sea Bottoms. 

Proc. Roy. Dublin Soc, N. S. IV, 277, 1884. 
— ,89. Buchanan, G. Y. The Guinea and Equatorial Currents. Geographi- 
cal Jour. VII, 269, London, 1896. 

— 90. Buchan, Alexander. Specific Gravities and Oceanic Circulation. 

Trans. Roy. Soc. Edinburgh. XXXVIII, 321, 1897. 

91. Lindenkohl, A. Oceanography. Ency lopedia Americana, 1904. 

92. Harris, R. A. Manual of Tides, Part V. U. S. Coast Surv. Rept. for 

1907. Appendix No. 6, p. 440, 1907. 

93. Ibid., pp. 437-438. 

94. Stevenson, Thomas. The Design and Construction of Harbours. 

3rd Edition, p. 91, Edinburgh, 1886. 

95. Mitchell, Henry. On the Circulation of the Sea through New 

York Harbor. U. S. Coast Survey Rept. for 1886, p. 431, 
1887. 

96. Gaillard, D. D. Wave Action in Relation to Engineering Structures. 

Corps of Engineers U. S. Army, Professional Paper No. 31, p. 91, 
Washington, 1904. 
-- 97. Kruger, Gustav. Uber Sturmfluten an der Deutschen Kiisten der 
Westlichen Ostsee mit Besonderer Berucksichtigung der Sturmflut 
vom 30-31 Dezember 1904. Jahresb. der Geogr. Gesells. zu Greifs- 
wald 1909-1910. XII, 259, 1911. 



154 CURRENT ACTION 

Wheeler, W. H. A Practical Manual of Tides and Waves, p. 76, 
London, 1906. 

98. Salisbury, R. D. Physiography, p. 728, New York, 1907. 

99. Harrington, M. W. Surface Currents of the Great Lakes. Bull. B., 

U. S. Dept. Agriculture, Weather Bureau, 1895. 

100. Dana, J. D. Manual of Geology. 4th Edition, p. 225, New York, 

1895. 

101. Harris, R. A. Manual of Tides, Part V, U. S. Coast Surv. Rept. for 

1907. Appendix No. 6, pp. 453-455, 1907. 

102. Ibid., p. 466. 

103. Ibid., p. 442. 

See also Grabau, A. W. Principles of Stratigraphy, p. 241, New York, 
1913. 

104. Harris, R. A. Manual of Tides, Part V, U. S. Coast Surv. Rept. for 

1907. Appendix No. 6, pp. 440, 454, 1907. 

105. Ekman, F. L. On the General Causes of the Ocean Currents. Nova 

Acta Regiae Societatis Scientiarum Upsaliensis . Serie 3, X, 47, 1876. 

106. Carpenter, W. B. Ocean Circulation. Contemporary Review. XXVI, 

567, 1875. 

107. Krummel, Otto. Handbuch der Ozeanographie. II. Die Bewegungs- 

formen des Meeres, p. 726, Stuttgart, 1911. 

108. Ruhl, Alfred. Beitrage zur Kenntnis der Morphologischen Wirk- 

samkeit der Meeresstromungen, pp. 3-9, Berlin, 1905. 

109. Pechuel, Loesche. Flachkusten, Meeresstromungen und Brandung. 

Globus, L, 39-42, 55-57, 1886. 

110. Salisbury, R. D. Physiography, p. 734, New York, 1907. 
Dana, J. D. Manual of Geology. 4th Edition, p. 230, 1895. 
Grabau, A. W. Principles of Stratigraphy, p. 244, New York, 1913. 

111. Willis, Bailey. Conditions of Sedimentary Deposition. Jour, of 

Geol. I, 484, 1893. 

112. Shield, William. Principles and Practice of Harbor Construction, 

p. 58, London, 1895. 

113. Whewell, W. Report on Discussions of Bristol Tides, Performed by 

Mr. Bunt under the Direction of the Rev. W. Whewell. Report of 
the British Assoc. XI, 33, 1842. 

114. Ekman, F. L. On the General Causes of the Ocean Currents. Nova 

Acta Regiae Societatis Scientiarum Upsaliensis. Serie 3, X, 32, 1876. 

115. Dawson, W. Bell. Note on Secondary Undulations Recorded by 

Self -registering Tide Gauges; and on Exceptional Tides in Relation 
to Wind and Barometer. Trans. Roy. Soc. Canada. I, Sec. 3, 26, 
Wheeler, W. H. A Practical Manual of Tides and Waves, p. 86, 
1895. London, 1906. 

116. Ekman, F. L. On the General Causes of the Ocean Currents. Nova 

Acta Regiae Societatis Scientiarum Upsaliensis. Serie 3, X, 11, 1876. 

117. Ibid., p. 11. 

118. Pettersson, Otto. On the Influence of Ice-Melting upon Oceanic 

Circulation. Svenska Hydrografisk Biologiska Kommissionens, Skrif- 
ter. 18 pp., Goteburg, 1905. J 



REFERENCES 155 

Pettersson, Otto. On the Influence of Ice Melting upon Oceanic 
Circulation. Geog. Journ. XXIV, 285-333, London, 1904. 

119. Sandstrom, J. W. On Ice-melting in Seawater and Currents Raised 

by It. Svenska Hydrografisk Biologiska Kommissionens, Skrifter. 
11 pp., Goteborg, 1905. 

120. Barnes, H. T. Report on the Influence of Icebergs and Land on the 

Temperature of the Sea. Dept. of Marine and Fisheries, 45th Ann. 
Rept., Supplement, 37 pp., Ottawa," 1913. 

121. Ekman, F. L. On the General Causes of the Ocean Currents. Nova 

Acta Regise Societatis Scientiarum Upsaliensis. Serie 3, X, 47, 1876. 

122. Harris, R. A. Manual of Tides, Part V. U. S. Coast Surv. Rept. for 

1907. Appendix No. 6, p. 441, 1907. 

123. Ibid., p. 441. 

124. Dawson, W. Bell. Report of Progress for the Year 1894 in the Sur- 

vey of Tides and Currents in Canadian Waters. Proc. Roy. Soc. 
Canada. I, p. XXII, 1895. 

125. Grabau, A. W. Principles of Str tigraphy, p. 241, New York, 1913. 

126. Otto, Theodor. Der Darss und Zingst. Jahresb. der Geogr. Gesells zu 

Greifswald. XIII, 363, 1913. 

127. Ekman, F. L. On the General Causes of the Ocean Currents. Nova 

Acta Regise Societatis Scientiarum Upsaliensis. Serie 3, X, 29, 1876. 

128. Pettersson, Otto. On the Influence of Ice-melting upon Oceanic 

Circulation. Svenska Hydrografisk Biologiska Kommissionens Skrif- 
ter, p. 15, Goteborg, 1905. 

129. Bjerknes, V. and Sandstrom, J. W. Uber die Darstellung des Hydro- 

graphischen Beobachtungsmateriales durch Schnitte, pp. 10, 18, 
Goteborg, 1901. 

130. Grabau, A. W. Principles of Stratigraphy, p. 240, New York, 1913. 

131. Fischer, Theobald. Zur Entwickelungs-Geschichte der Kiisten. 

Petermanns Geographische Mitteilungen. XXXI, 415, 1885. 

132. Maury, M. F. The Physical Geography of the Sea and its Meteor- 

ology, p. 184, London, 1881. 

133. Harris, R. A. Manual of Tides, Part V. U. S. Coast Surv. Rept. for 

1907. Appendix No. 6, p. 441, 1907. 

134. Murray, John and Hjort, Johan, et at. The Depths of the Ocean, 

pp. 285-287, London, 1912. 

135. Lindenkohl, A. Oceanography. Encyclopedia Americana, 1904. 
Harris, R. A. Manual rf Tides, Part V. U. S. Coast Surv. Rept. for 

1907. Appendix No. 6, p. 441, 1907. 

136. Murray, John and Hjort, Johan, et al. The Depths of the Ocean, 

p. 289, London, 1912. 

137. Reade, T. Mellard. Tidal Action as an Agent of Geological Change. 

Philosophical Magazine, XXV, 342, 1888. 

138. Ibid., p. 342. 

139. Buchan, Alexander. Specific Gravities and Oceanic Circulation. 

Trans. Roy. Soc. Edinburgh. XXXVIII, 327, 1897. 

140. Harris, R. A. Manual of Tides, Part V. U. S. Coast Surv. Rept. for 

1907. Appendix No. 6, p. 442, 1907. 



156 CURRENT ACTION 

Grabau, A. W. Principles of Stratigraphy, p. 241, New York, 1913. 
Krummel, Otto. Handbuch der Ozeanographie. II. Die Bewe- 
gungsformen des Meeres, p. 686, Stuttgart, 1911. 

141. Dall, W. H. Harbors of Alaska and the Tides and Currents in their 

Vicinity. U. S. Coast Surv. Rept. for 1872, p. 190, 1875. 

142. Geikie, A. Textbook of Geology. 4th Edition, p. 515, London, 1903. 

143. Le Conte. Elements of Geology. 2nd Ed., p. 40, 1882. 
Branner, J. C. The Pororoca, or Bore, of the Amazon. Science, IV, 

492, 1884. 

144. Ekman, F. L. On the General Causes of the Ocean Currents. Nova 

Acta Regise Societatis Scientiarum Upsaliensis, Serie 3, X, 16-37, 1876. 

145. Cornish, Vaughan. On Sea Beaches and Sand Banks. Geog. Jour., 

XI, 529, London, 1898. 

146. Ekman, F. L. On the General Causes of the Ocean Currents. Nova 

Acta Regise Societatis Scientiarum Upsaliensis. Serie 3, X, 23, 1876. 

147. Cronander, A. W. On the Laws of Movement of Sea Currents and 

Rivers, pp. 48-52, Norrkoping, 1898. 

148. Ekman, V. W. Ein Beitrag zur Erklarung und Berechnung des Strom- 

verlaufs an Flussmundungen. Kongl. Vetenskaps-Akademiens Ford- 
handlingar, pp. 479-507, 1899. 

149. Ibid., p. 501. 

150. Buchanan, J. Y. On the Land Slopes Separating Continents and 

Ocean Basins. Collected Papers. I, No. 39, 31 pp., Cambridge, 1913. 

151. Harris, R. A. Manual of Tides. Part V. U. S. Coast Surv. Rept. 

for 1907. Appendix No. 6, p. 356, 1907. 
Bache, A. D. On the Tidal Currents of New York Harbor near Sandy 
Hook. U. S. Coast Surv., Rept. for 1858, p. 200, 1859. 

152. Gulliver, F. P. Cuspate Forelands. Bull. Geol. Soc. Am. VII, 

413-417, 1896. 

153. Abbe; Cleveland, Jr. Remarks on the Cuspate Capes of the Caro- 

lina Coast. Proc. Bost. Soc. Nat. Hist. XXVI, 496-497, 1895. 

154. Vaughan, T. W. A Contribution to the Geological History of the 

Floridian Plateau. Carnegie Institution, Papers from the Tortugas 

Laboratory. IV, 142, 1910. 
Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 180, 1899. 
Hunt, E. B. On the Origin, Growth, Substructure, and Chronology 

of the Florida Reef. Am. Jour. Sci. 2nd Ser., XXXV, 198, 1863. 
Agassiz, Alexander. The Tortugas and Florida Reefs. Am. Acad. 

Mem. XI, 108, 1883. 

155. Perkins, F. W. [On the origin of the Florida counter current.] Per- 

sonal communication, 1914. 

156. Murray, John and Hjort, Johan, et al. The Depths of the Ocean, 

p. 270, London, 1912. 

157. Dall, W. H. Harbors of Alaska and the Tides and Currents in their 

Vicinity. U. S. Coast Surv., Rept. for 1872, p. 188, 1875. 

158. Harris, R. A. Manual of Tides, Part V. U. S. Coast Surv. Rept. for 

1907, Appendix No. 6, p. 442, 1907. 



REFERENCES 157 

- 159. Mill, H. R. The Clyde Sea-area. Trans. Roy. Soc. Edinburgh. 
XXXVI, 653, 1892. 

160. Ekman, F. L. On the General Causes of the Ocean Currents. Nova 

Acta Regiae Societatis Scientiarum Upsaliensis. Serie 3, X, 45-47, 
1876. 

161. Buchan, Alexander. Specific Gravities and Oceanic Circulation. 

Trans. Roy. Soc. Edinburgh. XXXVIII, 317-342, 1897. 
Ekman, F. L. On the General Causes of the Ocean Currents. Nova 
Acta Regiae Societatis Scientiarum Upsaliensis. Serie 3, X, 37-45, 1876. 

162. Parsons, H. de B. Tidal Phenomena in the Harbor of New York. 

Proc. Am. Soc. Civ. Eng. XXXIX, 659-670, 1913. 

163. Ekman, F. L. On the General Causes of the Ocean Currents. Nova 

Acta Regiae Societatis Scientiarum Upsaliensis. Serie 3, X, 32, 1876. 

164. Hunt, A. R. On the Action of Waves on Sea Beaches and Sea Bottoms. 

Proc. Roy. Dublin Soc, N. S. IV, 274, 1884. 

165. Cronander, A. W. On the Laws of Movement of Sea Currents and 

Rivers, pp. 15, 23, 31, Norrkoping, 1898. 

166. Harris, R. A. Manual of Tides, Part V. U. S. Coast Surv. Rept. for 

1907, Appendix No. 6, p. 356, 1907. 
__ 167. Otto, Theodor. Der Darss und Zingst. Jahresb. der Geogr. Ges. zu 
Greifswald. XIII, 362, 1913. 

168. Wheeler, W. H. The Sea Coast: Destruction: Littoral Drift: Pro- 

tection, p. 16, London, 1902. 

169. Hunt, A. R. On the Action of Waves on Sea Beaches and Sea Bottoms. 

Proc. Roy. Dublin Soc, N. S. IV, 241, 1884. 

170. Coode, John. Description of the Chesil Bank, with Remarks upon its 

Origin, the Causes which have Contributed to its Formation, and 
upon the Movement of Shingle Generally. Min. Proc Inst. Civ. Eng. 
XII, 593, 1853. 

171. Prestwich, Joseph. On the Origin of the Chesil Bank, and on the 

Relation of the Existing Beaches to Past Geological Changes Inde- 
pendent of the Present Coast Action. Min. Proc Inst. Civ. Eng. 
XL, 101, 1875. 

172. Ibid., p. 81. 

173. Ibid., p. 78. 

174. Palmer, H. R. Observations on the Motions of Shingle Beaches. Phil. 

Trans, of the Royal Society. CXXIV, Pt. I, 569, 1834. 

175. Prestwich, Joseph. On the Origin of the Chesil Bank, and on the 

Relation of the Existing Beaches to Past Geological Changes Inde- 
pendent of the Present Coast Action. Min. Proc. Inst. Civ. Eng. 
XL, 89, 1875 

176. Ibid., p. 89. 

177. Geikie, A. Textbook of Geology. 4th Edition, I, 576, 1903. 

178. Coode, John. Description of the Chesil Bank, with Remarks upon 

its Origin, the Causes which have Contributed to its Formation, and 
upon the Movement of Shingle Generally. Min. Proc Inst. Civ. 
Eng. XII, 540, 1853. 

179. Matthews, E. R. Coast Erosion and Protection, p. 6, London, 1913. 



158 CURRENT ACTION 

180. Shield, William. Principles and Practice of Harbor Construction, 

p. 41, London, 1895. 

181. Kinahan, G. H. The Travelling of Sea Beaches. Min. Proc. Inst. 

Civ. Eng. LVIII,. 281, 1879. 

182. Palmer, H. R. Observations on the Motions of Shingle Beaches. 

Phil. Trans, of the Royal Society. CXXIV, Pt. I, 571, 1834. 

183. Coode, John. Description of the Chesil Bank, with Remarks upon 

its Origin, the Causes which have Contributed to its Formation, and 
upon the Movement of Shingle Generally. Min. Proc. Inst. Civ. 
Eng. XII, 540, 1853. 

184. Reade, T. Mellard. Tidal Action as an Agent of Geological Change. 

Philosophical Magazine. XXV, 342, 1888. 
Dana, J. D. Manual of Geology. 4th Edition, p. 229, 1895. 

185. Mitchell, Henry. The Under-run of the Hudson River. U. S. Coast 

Surv. Rept. for 1887, p. 301, 1889. 

186. Harris, R. A. Manual of Tides, Part V. U. S. Coast Surv. Rept. for 

1907, Appendix No. 6, p. 442, 1907. 

187. Wheeler, W. H. The Sea Coast: Destruction: Littoral Drift: Pro- 

tection, pp. 23-25, London, 1902. 



CHAPTER IV 
TERMINOLOGY AND CLASSIFICATION OF SHORES 

Advance Summary. — Before undertaking a systematic dis- 
cussion of shoreline development it is important to adopt a 
satisfactory terminology for the topographic elements of shores, 
and to agree upon a classification of shorelines which shall serve 
as a guide throughout this treatment. These are the two tasks 
attempted in the present chapter. With the aid of explanatory 
diagrams the terminology used in this volume is made clear. 
The discussion of shore terminology leads inevitably to a con- 
sideration of the terminology of peneplanes of marine and other 
origins, and space is given to an inquiry into the proper signifi- 
cance of the terms plains, planes, and peneplanes. The classifi- 
cation of shorelines is next essayed. After a brief review of 
previous methods of classification, a genetic scheme is adopted 
in which four primary types of shoreline are recognized. These 
are described, their chief subdivisions named, and, where cir- 
cumstances make it advisable, discussed at some length. It is 
further pointed out that each class or sub-class of shorelines 
passes through its appropriate young, mature and old sequential 
stages of development. 

Terminology of Shores. — The line where land and water meet 
has been called the shoreline, the strandline, the coast line, and 
the water line. The terms shore, beach, strand, and coast are 
also loosely used with Varying significance by different writers. 
" Shore " is defined by Gulliver 1 as the water area immediately 
seaward from the shoreline; by modern legal authorities, as the 
space between low water and high water; and by Wheeler 2 , as the 
land area immediately above high water. " Beach " is sometimes 
used to denote the zone between low water and high water, or 
to denote the debris found between those limits, while others 
regard it as extending some distance below low water. " Coast " 
may mean the narrow strip immediately landward from the 
shoreline 3 , or it may imply a much broader zone extending some 
distance inland. Ratzel 4 discusses at some length the varying 

159 



160 TERMINOLOGY AND CLASSIFICATION OF SHORES 



significance attached to the word coast by different writers. Evi- 
dently there is a variety of usage in naming shore features, even 
among scientific workers. It is essential, therefore, that we adopt 
a terminology to be used throughout this discussion, and an 
effort will be made to secure the required precision with the least 
possible departure from common usages. 

At the margin of the sea there are typically found three or four 
distinct zones, each of which is characterized by certain peculiar 
forms due to deposition or erosion. The zones, the erosion fea- 
tures, and the features due to deposition must each be clearly 
distinguished and receive appropriate names (Figs. 22 and 23). 
The most important of the four zones extends from low water 
mark to the base of the cliff, whether large or small, which 




Fig. 22. — Elements of the shore zones during an early stage of development. 

usually marks the landward limit of effective wave action. This 
is the zone over which the water line, the line of contact between 
land and sea, migrates; and it will here be called the shore. It 
is, indeed, the zone most commonly referred to when the word 
shore is employed in ordinary speech, and is likewise the zone 
defined as the shore in Roman law. 

Landward from the shore is a much broader zone of indeter- 
minate width, which will here be called the coast. While some 
may have more or less consciously included the shore when 
referring to a coast, it is also quite common to exclude it, by 
implication at least, as when one says that a coast terminates 
in a series of ragged cliffs. Indeed, the narrow shore zone is 
probably seldom thought of when a coast is referred to, and it 
will conduce to clearness if we restrict the terms shore and coast 
to the two independent zones. The line which forms the bound- 
ary between these zones is the coast line, and it marks the sea- 
ward limit of the permanently exposed coast. In a correspond- 



TERMINOLOGY OF SHORES 161 

ing manner the low tide shoreline marks the seaward limit of the 
intermittently exposed shore. The position of the water line at 
high tide marks the high tide shoreline. When the term " shore- 
line " alone is used in the text, low tide shoreline is to be under- 
stood. 

Seaward from the low tide shoreline is a narrow zone per- 
manently covered by water, over which the beach sands and 
gravels actively oscillate with changing wave conditions. Al- 
though of great importance to the student of shores, this zone 
has no suitable name. Gulliver 5 recognized this difficulty, and 
proposed to call the zone the " shore"; but his suggestion is 
hardly acceptable in view of the fact that " shore " is almost 
universally applied to some part of the land area inside the low 
water mark. Gulliver, furthermore, recognized only two zones, 
the coast and the shore. " Inshore " is sometimes used as 
opposed to " offshore," but is quite uniformly applied to a broader 
zone than that now under consideration; as, for example, in 
the expression " inshore fishing," which may refer to fishing 
carried on from one to three miles from the land. The term 
" shore face " as used by Barrell 6 in his discussion of deltas 
applies to much of the zone here in question, and after confer- 
ence with that author I have decided to adopt his term, writing 
it as one word, shoreface, and redefining it as the zone between 
the low tide shoreline and the beginning of the more nearly 
horizontal surface included in the zone next defined. Extending 
from the outer margin of the rather steeply sloping shoreface to 
the edge of the continental shelf is a comparatively flat zone 
of variable width which will be called the offshore belt, or simply 
the offshore (Fig. 23). This is the zone commonly referred to 
in such expressions as " offshore sediments," and " offshore 
deposition." 

The shore is sub-divided into two minor zones. One of these 
lies between the ordinary high and low water marks, and is 
daily traversed by the oscillating water line as the tides rise and 
fall. This zone is already well known as the foreshore. Back of 
it is the portion of the shore covered by water during exceptional 
storms only, which I propose to call the backshore. 

The wave-erosion features associated with the coast, shore, 
shoreface, and offshore, are three in number. At the seaward 
edge of the coast is the wave cut cliff, which varies in magnitude 



162 TERMINOLOGY AND CLASSIFICATION OF SHORES 



Coast 



from an inconspicuous slope at the 
margin of a low coastal plain or in the 
side of a sand dune, to an escarpment 
hundreds of feet in height. In front of 
it, and occupying all of the shore zone 
and part or all of the shoreface is the 
wave cut bench, a sloping erosion plane 
inclined seaward. The bench may end 
abruptly at the top of a steeper slope 
representing part of the original surface 
of the sea-bottom (Fig. 22); or it may 
gradually decrease in slope until it 
merges imperceptibly into the more ex- 
tensive, nearly horizontal plane pro- 
duced by long continued wave erosion, 
which is commonly called the abrasion 
platform (Fig. 23). 

There are three characteristic de- 
posits which rest upon the wave cut 
bench and the slopes which lie to sea- 
ward of it. Most important of these 
is the deposit of material which is in 
more or less active transit, along shore 
or on-and-off shore, and which will be 
called the beach. Gilbert 7 defined the 
beach as " the zone occupied by the 
shore drift in transit." It seems to 
the present writer that the descriptions 
of beaches given by that careful and 
scholarly investigator of the topo- 
graphic features of lake shores really 
deal with the deposits, and not with 
the zone in which those deposits occur; 
and what I have suggested is therefore 
a difference in phraseology rather than 
a real difference of interpretation. It 
would be unfortunate to have two 
names for the same zone, and none for 
the deposit which may or may not 
occur in that zone, as would be the 



TERMINOLOGY OF SHORES 163 

case if we accepted Gilbert's definition literally; for the zone 
over which material is in transit certainly includes the shore, 
and the transit of the material may either be so slow that some 
of it accumulates to form a deposit within the shore zone, or so 
rapid that bare rock is continuously exposed there (Fig. 22). 
Furthermore, the term " beach," as originally used, referred to 
the " shingle " or pebbles found on many of the English shores, 
and is employed in this sense in some parts of England to the 
present day. 

Near the edge of the wave cut bench a portion of the beach is 
often fashioned into a terrace which is for a time progressively 
built out into the deeper water, only to be later modified or 
destroyed during heavy storms. This wave-built terrace may 
be called the shoreface terrace to distinguish it from a series of 
terraces caused by the action of storm waves on the upper part 
of the beach, and which we will call the backshore terraces (Fig. 23). 
As the abrasion platform is developed it may be covered with a 
thin deposit of material in slow transit, which constitutes the 
veneer. At the outer margin of the abrasion platform there accu- 
mulates an extensive deposit of the material which has been 
moved across the platform to a more permanent resting place in 
the deeper, quieter water beyond. This we will call the conti- 
nental terrace; together with the abrasion platform it makes the | 
continental shelf. 

It will be shown in the following chapter that if a land mass 
stands still long enough, the waves will reduce it to an ultimate 
abrasion platform; and this is true, no matter how great may 
have been the original extent of the land. The final stage of 
shore development will witness the extinction of all of the above 
mentioned features, except only the abrasion platform and the 
continental terrace. Even the veneer may be removed and 
the bare rock surface of the platform exposed. Should an uplift 
raise the platform high above sealevel, stream erosion might 
dissect the new land area until only remnants of the former 
smooth erosion surface would be left. There are many dis- 
sected erosion surfaces in the world, some of which probably 
represent uplifted abrasion platforms. If the platform were 
reduced practically to a plane surface before uplift, the uplifted 
surface may be called a plane of marine denudation, or simply 
a marine plane. On the other hand, if wave erosion had not 



164 TERMINOLOGY AND CLASSIFICATION OF SHORES 

yet succeeded in perfecting a smooth plane when uplift raised 
the platform above the reach of the waves to form a land area, 
the uplifted surface should be called a marine peneplane. These 
last two terms involve a slight revision of former usage, which 
cannot be appreciated without some consideration of the ter- 
minology of erosion planes in general. We may therefore turn 
our attention for a few moments to this broader subject. 

Plains, Planes, and Peneplanes. — In an erosion cycle of any 
kind a land mass will in time be worn down to a smooth surface, 
providing the process of erosion is not interrupted. Long con- 
tinued wave erosion reduces the land to a plane below sealevel; 
long continued stream erosion, to a plane at sealevel; and long 
continued wind erosion, to a surface at some elevation above 
the sea which will then be progressively lowered until sealevel is 
reached. Long continued glacial erosion may possibly produce 
a plane or a concave surface, either above or below sealevel; 
but the cycle of glacial erosion is not so well understood as are 
the other three cycles mentioned. 

The work of any erosive force may be interrupted after the 
land has been worn down to a gently undulating surface of low 
relief, but before complete planation has been accomplished. 
We must recognize, therefore, not only the plane surfaces of 
ultimate erosion, but imperfect, " almost-plane " surfaces which 
characterize the penultimate stages of the several cycles. Theo- 
retically, at least, there may be three, or possibly four, planes 
of erosion, with a corresponding number of almost-plane sur- 
faces of uncompleted erosion, due to the action of rivers, waves, 
winds, and possibly glaciers. 

Davis has given the name " peneplain " to the almost-plane 
surface of uncompleted fluvial denudation. The other almost- 
plane surfaces remain unnamed, except that such terms as " plain 
of marine denudation," " plain of marine abrasion," and " plain 
of aeolian erosion " have been applied to erosion surfaces, 
usually without regard to the question whether they were really 
plane surfaces, or only surfaces of moderate relief. An exception 
to the foregoing statement is perhaps to be found in Gulliver's 
valuable paper on " Shoreline Topography," where he seems to 
call the almost plane surface of marine erosion a " submarine 
platform," although he makes it identical with " plain of marine 
denudation," and would therefore seem to have no name for a 



PLAINS, PLANES, AND PENEPLANES 165 

perfectly plane surface of marine denudation 8 . It does not seem 
advisable to apply the adjective " submarine " to a surface which 
is today far above sealevel, so some other name should be 
sought for up-lifted surfaces of marine erosion. 

It is coming to be recognized that some of the so-called pene- 
plains are more probably almost-plane surfaces of marine erosion, 
as was, indeed, the opinion of the earlier geologists. Barrell 9 
has even questioned the subaerial origin of the New England 
uplands, supposedly a typical peneplain, and the one above which 
rises the mountain selected as the type " monadnock." Should 
his conclusions prove correct, and apply to the portion of the 
supposed peneplain in southern New Hampshire, then not only 
would the upland cease to merit the term " peneplain," but Mt. 
Monadnock would no longer be a " monadnock," as that term 
is generally defined. We would have to change the definition 
of monadnock, or invent a new name for the topographic feature 
of which it is an example. 

A further difficulty arises from the fact that the word " plain " 
is used for two such very different conceptions as a plane of 
ultimate erosion, and a series of low-lying horizontal sediments 
which may be dissected into hills and valleys by stream erosion. 
A peneplain is not " almost a plain " of the second type, but 
is almost a plane surface in the mathematical sense of the 
term. 

It appears, therefore, that we need names for the different 
types of erosion surfaces which theoretically may be produced 
both in the penultimate and the ultimate stages of erosion; 
that we also need a name for the actually existing upland sur- 
faces of erosion which are so abundant in different parts of the 
world but of whose origin we are not yet certain; and, finally, 
that we need a clearer distinction in the names themselves, 
between lb plains " of erosion, " plains " of deposition, and 
" peneplains." I believe it is possible to meet all these needs 
without departing unduly from the path of conservatism; and 
to this end the following usage will be adhered to in future 
pages: (1) The level erosion surface produced in the ultimate 
stage of any cycle will be called a plane. (2) The undulating 
erosion surface of moderate relief produced in the penultimate 
stage of any cycle will be called a peneplane. (3) A low-relief 
region of horizontal rocks will be called a plain. We. may then 



166 TERMINOLOGY AND CLASSIFICATION OF SHORES 

recognize planes of fluvial,* marine, aeolian, and glacial denuda- 
tion; also fluvial peneplanes, marine peneplanes, aeolian pene- 
planes, and glacial peneplanes. A monadnock may be defined 
as an erosion remnant left standing above a peneplane of any 
origin, either because it is composed of more resistant rock 
or because it has been less exposed to the agents of erosion. 
Vogt 10 has already used the term " Monadnock-Berge " for 
isolated hills on the uplifted marine abrasion plane of northern 
Norway. It seems desirable to employ a special term for a 
surface of marine denudation which is still in its original po- 
sition at or near wave base, with the marine forces still operating 
on it, and for this feature the name abrasion platform has al- 
ready been used. An uplifted abrasion platform of large areal 
extent is a marine peneplane or a marine plane, according to the 
smoothness of the surface produced by wave erosion. 

The advantages of this usage are obvious. It tends to sim- 
plify, not to complicate physiographic terminology. The origin 
of any of the level or almost level surfaces here discussed is at 
once apparent from the spelling. If in describing a coastal 
region one uses the otherwise non-commital term " marine plain,", 
in the manner here suggested, the reader knows at once that a 
coastal plain of marine sediments is referred to; while " marine 
plane " indicates a wave-cut plane surface. When we remember 
that both of these forms have been called " marine plains," 
the advantage of the distinction in spelling is evident. One of 
our ablest geographers has applied to a wave-cut rock bench 
along the coast the term " coastal plain." Had he written 
" coastal plane " his meaning at least would have been clear, 
even though the term as a whole might still be criticized. A 
peneplain is not " almost a plain " of horizontal sediments, but 
is almost a plane surface in the mathematical sense of the term; 

* " Subaerial" denudation was long used for "fluvial" denudation, be- 
cause of the prevalent idea that there were only two important types of 
denudation, subaerial and submarine. Since the importance of aeolian 
denudation, which is also subaerial, has been recognized, it is desirable to 
distinguish the two types of subaerial denudation by the terms "fluvial" 
and " aeolian." It should be understood that the term fluvial is here used 
in its broadest sense, to include the action of rain water assisted by weather- 
ing and all other forces causing streams of water and waste from the largest 
to the smallest dimensions. Fluvial denudation is in reality pluvio-fluvial 
denudation. 



PLAINS, PLANES, AND PENEPLANES 167 

therefore, " peneplane " more clearly expresses the true meaning 
of the term than does the older and commoner spelling. So 
standard a text as Dana's " Manual of Geology " employs the 
spelling " peneplane " u , while J. W. Gregory 12 in his recent book 
on "The Nature and Origin of Fiords " makes use of the same 
form. Lawson has employed both spellings, the form " pene- 
plane " occurring in his "Post-Pliocene Diastrophism of the Coast 
of Southern California " 13 . It may be, also, that the combination 
of "plane" with "pene-" will seem less objectionable to those 
who dislike hybrid terms, since " plane " is closer to the original 
Latin form than " plain." 

Davis's introduction of " peneplain " into the vocabulary of 
physiography in 1889 14 was a valuable service to the science; 
for it led to a speedy and world-wide recognition of a conception 
which had previously been announced by Marvine 15 and ex- 
tensively developed by Powell 16 and Dutton 17 , but which did not 
become current until well named. It should be appreciated, 
however, that at this time the idea of subaerial denudation was 
supplanting, rather than supplementing, the idea of marine 
denudation. The general attitude was well expressed by de 
Lapparent 18 in the words: " La notion des peneplaines est ex- 
trement feconde, et ce n'est pas un de ses moindres merites 
d'avoir porte le coup de grace a la theorie des plaines de denu- 
dation marine, si fort en honneur de l'autre cote du detroit." 
Davis himself regarded extensive planes of marine denudation 
as " very improbable " 19 , while planes of glacial or aeolian denu- 
dation were as yet scarcely considered. All planes of penul- 
timate stages of erosion were called " peneplains," because it 
was believed that they were all formed essentially by subaerial 
agencies. No need was felt of names for almost-plane surfaces 
of marine and other types of erosion, since the existence of such 
planes was either considered improbable, or was not considered 
at all. 

Later years have witnessed the publication of Passarge's 
studies of surfaces of aeolian denudation 20 , and the probability 
of the existence of fairly extensive surfaces of marine denudation 
seems now to be recognized by Davis and others 21 . We are 
confronted with the fact that there are numerous all-most plane 
erosion surfaces in various parts of the world, the origin of which 
is in most cases doubtful, and in many cases will probably never 



168 TERMINOLOGY AND CLASSIFICATION OF SHORES 

be known because nearly all of the upland has been destroyed 
by subsequent stream erosion. As Davis once remarked, "It 
must be remembered that the terms ' plain of marine denudation ' 
and ' peneplain ' are in nearly all cases hardly more than dif- 
ferent names for the same thing. If the whole truth were known, 
it is probable that one or the other name might be appropriately 
applied in this or that case, but it is seldom that anyone has suc- 
ceeded in convincing all his contemporaries that he could dis- 
tinguish a plain of marine denudation from a peneplain, or vice 
versa " 22 . Present needs can better be met by applying the 
excellent term " peneplane " to all these surfaces, and qualifying 
the term by the word fluvial, marine, aeolian or glacial in case 
it can be shown that a given surface is of the origin indicated by 
the qualifier, rather than by inventing a new term for almost- 
plane erosion surfaces of doubtful origin. Peneplane is too valu- 
able a term, and is too extensively used, to have it restricted to the 
very few (if any) erosion surfaces demonstrably of fluvial origin; 
and since the wise physiographer must avoid a name which 
commits him unwillingly to a certain theory of origin, it is best in 
the present case to extend the meaning of the term. 

While it is true that I am advocating a broader significance for 
" peneplane " than is usually given to it, precedent for such 
usage is not altogether lacking. H. E. Gregory 23 is respon- 
sible for using " peneplain " as synonymous with " plain of 
denudation . . . carved out of other land forms either by the 
action of the forces that work on the land or by the waves of the 
sea." Davis himself has occasionally employed the term in the 
broader sense. Thus, in an account of the geographic develop- 
ment of Northern New Jersey, he discusses at length " whether 
the old Highland peneplain was the product of subaerial or sub- 
marine processes" 24 . He distinguishes between "subaerial base- 
level plain" and "submarine platform," but applies the name 
" peneplain " to the topographic feature itself while its origin 
remains in doubt. In a discussion of the arid cycle by the 
same author 25 " peneplains " are usually contrasted with true 
" plains " of aeolian erosion; but the frequent use of the ex- 
pression " normal peneplain," and the application of the term 
" monadnock " to residuals on a plane of aeolian denudation, 
suggest that the author at least unconsciously recognized the 
possible existence of " peneplains " which were not formed by 



CLASSIFICATION OF SHORELINES 169 

" normal " (stream) erosion. Marine peneplanes are more defi- 
nitely recognized, at least as a theoretical possibility requiring 
discussion, when in an essay on planes of marine and subaerial 
denudation the author says: " By whatever process the so-called 
' plain of denudation ' was produced, an explanation that will 
account for a peneplain of moderate or slight relief is all that 
is necessary " 26 . 

Recognition of the fact that wave erosion is capable of produc- 
ing a marine plane, or at least a marine peneplane, is essential to a 
full comprehension of some significant phases of shoreline activity. 
This matter will claim our attention in the next chapter. 

Classification of Shorelines. — Various classifications of shore- 
lines or coasts have been proposed, some of which are based on 
form rather than genesis, while others take account of the origin 
of shorelines but do not consider the stages of development 
reached since they originated. The first type of classification is 
wholly empirical and therefore not very significant; the second 
type is partly genetic, but not evolutionary, and is therefore less 
significant than it might be. Neither type permits one to ar- 
range all shore forms in genetic series according to their relative 
advance in the cycle of shoreline evolution. Good examples 
of such classifications will be found in Suess' " Das Antlitz der 
Erde " 27 , von . Richthofen's " Fiihrer fur Forschungsreisende " 28 , 
and Penck's " Morphologie der Erdoberflache " 29 . Those desiring 
to study further the methods of classification here referred to will 
profit from a reading of Fischer's paper entitled "Zur entwickel- 
ungs-geschichte der Kusten " 30 , and Hahn's paper on " Ku- 
steneinteilung und Kustenentwickelung im verkehrsgeographis- 
chen Sinne " 31 . Applications of such methods in the description 
of specific coasts have been made by Haage 32 in his dissertation 
on " Die Deutsche Nordseekiiste," by Meinhold 33 in an essay 
entitled " Die Kiiste der mittleren atlantischen Staaten Nor- 
damerikas," and by Weidemuller 34 in his account of " Die 
Schwemmlandkusten der Vereinigten Staaten von Nordamerika." 
American students will be especially interested in the last two 
papers, since they relate to our own shores and at the same time 
furnish good examples of a type of physiographic description 
very commonly encountered in German writings. The details 
of coastal features are empirically described with painstaking 
care and at great length, instead of being represented by maps; 



170 TERMINOLOGY AND CLASSIFICATION OF SHORES 

and while the origin of the features so described is then con- 
sidered, each coast section is for the most part treated as a 
special isolated problem, without regard to its position in a 
series of sequential forms. 

Numerical Methods. — Many attempts have been made to ex- 
press the distinctions between different types of coasts in numeri- 
cal terms. This method has been much in vogue among German 
students since the time of Ritter. The essential object of the 
method is to establish a comparison between coasts showing differ- 
ent degrees of indentation by the sea, and the comparison is usually 
expressed by a numerical relation rather than by absolute figures, 
such as the actual length of shoreline. Various relations have 
been utilized in this connection, such as the ratio existing between 
the length of the actual shoreline and the shortest possible shoreline 
which the area in question could have (Nagel); or the ratio of 
actual shoreline length to the length of an ideal contour con- 
necting the outer points of the peninsulas, or the innermost 
points of the bayheads; or the ratio between the area of the 
main continental mass and the area of the outlying peninsulas 
and islands (Kloden) . Ritter 35 and Berghaus 36 compared the area 
of the land with the length of the bordering shore, a method which 
was criticized by mathematicians on the ground that planes could 
not properly be compared with lines. Nagel 37 determined the 
size of a circle containing the same area as the land whose coast 
was under examination, and then compared the length of actual 
shoreline with the circumference of this circle. 

Schwind 38 employs a comparison between the length of actual 
shoreline and the length of a selected isobath having a much 
simpler form, thus following the method of his teacher, Ratzel 39 , 
who considers that the length of the shoreline should always 
be compared with some real contour-line. De Martonne 40 
presents a number of valid criticisms against all these methods, 
and suggests that more significant results can be obtained by 
comparing lengths of shoreline with areas included between 
selected contours above and below sealevel. 

These are but a few of the great number of schemes devised by 
different students in an attempt to discover a method which 
would not be open to the criticisms urged by each student against 
all the methods of his predecessors. We must restate today 
Hahn's conclusion 41 of a third of a century ago, that all numerical 



CLASSIFICATION OF SHORELINES 171 

methods of coast description are failures. All of them' are es- 
sentially empirical, and hence of little or no significance to the 
student of shore forms. They tell little which a good map does 
not tell much better. Even when the numerical expression is 
combined with a discussion of the relation of the shoreline to 
geological structure, changes of level, the progress of shore 
accretion, and other phenomena affecting the coast, the result 
is a description only partially genetic, and one which fails to 
recognize the importance of shore processes in developing the 
shoreline in orderly, sequential stages. 

The reader who would examine further the numerical schemes 
for coastal description will find a good historical review of the 
development of the method in Riessen's " Uberblick und Kritik 
der Versuche Zahlenausdrucke fur die grossere oder geringere 
Kiistenentwickelung eines Landes oder Kontinentes zu fin den" 42 
while Schwind's essay on " Die Riaskusten und ihr Verhaltnis 
zu den Fjordkiisten unter besonderer Berucksichtigung der 
horizontalen Gliederung/' 43 contains a bibliography of the sub- 
ject. Reference should also be made to the paper by de Mar- 
tonne 44 already mentioned and to other papers by Reuschle 45 , 
Schroter 46 , and Hentzschel 47 where special applications of the 
method are considered. A good idea of the ingenious but highly 
artificial and complex mathematical methods of describing coastal 
embayments employed by Weule, Guttner, and others may be 
secured from Giittner's dissertation on " Geographische Ho- 
mologien an den Kusten mit besonderer Berucksichtigung der 
Schwemmlandkusten " 48 . Descriptions of the southeastern coast 
of the United States based in part on numerical methods will be 
found in reports by Weule 49 and Weidemiiller 50 . 

Genetic Classification of Shorelines. — The character of any shore- 
line must depend in the first instance upon the character of the 
land surface against which the sea comes to rest. If the surface 
is a partially submerged, irregularly dissected land area with 
numerous hills and valleys, the water will enter the branching 
valleys and spread around the hills, forming a very complicated 
shoreline. If the surface is a smooth, emerged sea-bottom, the 
shoreline is necessarily simple. It follows from this that the 
most significant classification of shorelines will be one which takes 
account of the nature of the movements of land or water which 
brought the water surface against the land at the present level. 



nr^ 



172 TERMINOLOGY AND CLASSIFICATION OF SHORES 

It was upon such a genetic basis that Davis 51 divided shorelines 
into two primary classes, and that the more detailed discussion 
of Gulliver 52 was founded. There are, however, important shore- 
lines which find no satisfactory place in the classifications of Davis 
and Gulliver, and for which provision must be made. 

We will find it profitable to divide shorelines into four main 
classes: I, Shorelines of submergence, or those shorelines pro- 
duced when the water surface comes to rest against a partially 
submerged land area; II, Shorelines of emergence, or those result- 
ing when the water surface comes to rest against a partially 
emerged sea or lake floor; III, Neutral Shorelines, or those whose 
essential features do not depend on either the submergence of 
a former land surface or the emergence of a former subaqueous 
surface; IV, Compound Shorelines, or those whose essential 
features combine elements of at least two of the preceding classes. 

Shorelines of submergence have been called " shorelines of 
depression"; but this implies a depression of the land, whereas 
the submergence may as well result from a rising of sea or lake 
level, or from the melting of tidewater glaciers permitting sub- 
mergence of glacial troughs without any change in the relative 
level of either land or water. The term " shorelines of emergence " 
is likewise preferable to " shorelines of elevation," not only be- 
cause emergence may result from the lowering of sea or lake 
surface, but for the added reason that " shorelines of elevation " 
and " elevated shorelines," two wholly distinct forms, are in 
danger of having their similar titles confused even though there 
is no possibility of confusing the forms themselves. The terms 
" sinking " and " rising " have been applied to coasts bordered 
by shorelines of submergence and shorelines of emergence; and 
in his admirable treatise on " Die Erklarende Beschreibung der 
Landformen " Davis 53 classifies the coasts, rather than the shore- 
lines, into Senkungskiisten and Hebungskusten. Such terms are 
open to the objection that they not only imply an actual change 
of level, and that it is a land movement which effects this change, 
but also that the movement is still going on; three implications 
which are probably not justified in the case of many coasts to 
which the terms are applied. We might employ the terms 
" positive shorelines " and " negative shorelines," thus indicating 
that the shorelines resulted from positive or negative movements 
of the water line, without indicating whether such movements 



SHORELINES OF SUBMERGENCE 173 

resulted from changes in the level of the land or the water. But 
these terms are open to two objections: they have been applied 
to land movements as well as to strand movements, and many 
are confused by the necessity of remembering that a positive 
land movement means a negative strand movement, whereas 
a positive water movement means a positive strand movement; 
furthermore, they imply that some vertical change in either land 
or water is necessary, whereas we have seen that submergence 
may occur with no change in the level of either. " Irregular 
shorelines " and " simple shorelines " are unsatisfactory, both 
because they are empirical terms which carry no suggestion of 
origin, and because all classes of shorelines are simple in mature 
or late mature stages of development. " Shorelines of sub- 
mergence " and " shorelines of emergence " are explanatory 
terms; they are genetic rather than empirical ; they do not carry 
any implication as to whether it is the land or the sea which 
moves, and do not even imply any vertical change of level in 
either; they are easily understood, and are not in danger of being 
confused with other terms applied to shoreline phenomena. For 
these reasons it seems desirable to use them instead of the other 
terms which have been mentioned. 

I. Shorelines of submergence may be subdivided into two 
main types, according to the nature of the forms submerged. 
These are : (a) shorelines formed by the partial submergence of a 
land mass dissected by normal river valleys, which may be called 
ria shorelines, after the ria coast of northwestern Spain, which was 
produced by the drowning of normal river valleys along a moun- 
tainous coast; thus used, the term ria is not restricted to the 
narrow meaning assigned to it by von Richthofen, who first used 
it in a generic sense; but is employed in the broader sense in 
which it has been used by Gulliver and others : (6) shorelines pro- 
duced by the partial submergence of a region of glacial troughs, 
known as fjord shorelines, like those of Norway and Alaska. 

(a) Ria Shorelines. Since ria shorelines are produced by the 
partial submergence of normally dissected examples of the three 
main groups of constructional landforms (plains-plateaus, moun- 
tains and volcanoes), we may recognize as three subtypes: 
embayed plain or plateau shorelines, such as are found in the 
Chesapeake Bay region (Fig. 24) ; embayed mountain shorelines, of 
which the Maine coast and the coast of Brittany furnish good ex- 



174 TERMINOLOGY AND CLASSIFICATION OF SHORES 




SHORELINES OF SUBMERGENCE 175 

Plate XVI. 




Hornviken, a small fjord near Nortn Cape, Norway, showing typical over- 
steepened walls of a glacial trough. 



176 TERMINOLOGY AND CLASSIFICATION OF SHORES 

amples; and embayed volcano shorelines, a number of which are 
found in the South Pacific, having been cited by Dana 54 in support 
of Darwin's theory of a subsidence of that ocean's floor. When 
desirable, the form of the shoreline may be more clearly in- 
dicated by specifying the particular type of plain, plateau, 
mountain, or volcano involved. Thus one may speak of the 
embayed coastal plain shoreline of Maryland, or the embayed 
folded mountain shoreline of the Adriatic coast of Dalmatia, 
thereby taking due account of the structure of the thing sub- 
merged, which is an important element in determining the 
character of any shoreline of submergence. 

T^are must be taken to avoid the ancient fallacy that the 
branching bays of ria coasts are due to wave and tidal erosion 55 . 
It is illustrative of the slow progress of the science of shorelines 
that Playfair, at the same time that he made his keen obser- 
vations on the nature and origin of river valleys, should ascribe 
deep gulfs and salient promontories to differential wave erosion, 56 
and that nearly a century later Fischer 57 and other students of 
shorelines should be found still advocating this view. Al- 
though it was recognized some time ago that as a rule tidal cur- 
rents merely ebb and flow through submerged branching river 
valleys which they had no power to originate and which or- 
dinarily they have but very moderate power to enlarge, and that 
wave erosion tends to obliterate the larger irregularities of a 
coast and not to make them, one still finds the tidal and wave 
origin of such drowned valleys as those of the Maine coast 
maintained in recent editions of a standard textbook on geology 58 . 

(b) Fjord Shorelines. — Perhaps no type of shoreline has given 
rise to so much discussion as has the fjord shoreline. We may 
note in the first place that geologists and geographers may be 
divided into two main groups whose ideas regarding the origin 
of fjords are mutually opposed. The first group may be desig- 
nated as the " glacialists, " because in their opinion all the 
phenomena peculiar to fjords may be explained as the result of 
extensive glacial over-deepening of pre-glacial river valleys near 
the sea. The second group, or " non-glacialists," reject the 
theory of ice erosion, and attempt to account for the phenomena 
of fjords in other ways. 

According to the glacial theory, fjords are partially submerged 
glacial troughs. The troughs of glaciated mountains far from 




Fig. 25. — A typical section of the fjord coast of Norway, showing angular 

pattern attributed to fault-control. (177) 



178 TERMINOLOGY AND CLASSIFICATION OF SHORES 



Plate XVII. 




Photo by Underwood & Underwood. 

Idde Fjord near Fredriksten, Norway, showing rectangular pattern char- 
acteristic of many fjord coasts. 



SHORELINES OF SUBMERGENCE 179 

the sea are similar to fjords, except that the former have not 
been drowned by marine waters. In both cases the troughs were 
formed by extensive glacial over-deepening of former river val- 
leys. The pre-glacial valleys guided the glaciers which later 
came to occupy them, and by confining the ice streams to the 
narrow limits imposed by the valley walls, insured a maximum 
efficiency of glacial erosion. The glacial theory asks no questions 
as to what determined the courses of the pre-glacial valleys; 
but it is fully recognized that among other causes ancient fault 
lines must be considered, since a fault may give a crushed zone 
which is weaker than the unfractured rock, or may bring a belt 
of weak rock into such position that subsequent valleys will 
soon be excavated along it, parallel to the fault. This would 
satisfactorily account for the fact that many fjord shorelines have 
a more or less angular pattern. (Fig. 25 and Plate XVII). 

Esmark 59 was the first to advocate the glacial origin of fjords, 
almost a century ago. The fjord valleys of New Zealand were 
ascribed largely to ice erosion by von Haast 60 in 1865, while 
Helland 61 a few years later, in discussing the fjords of Norway 
and Greenland, gave the best exposition of the glacial theory as 
applied to the interpretation of fjords which had appeared up 
to that time. Helland seems to have anticipated Shaler in 
recognizing the ability of glaciers to excavate their channels 
below sealevel, and to have given a fairly good account of the 
essential significance of hanging valleys some twenty years be- 
fore Gannett's classic statement. The influence of rock frac- 
tures on the orientation of fjord valleys was recognized by 
Brogger 62 , who did not fail, however, to attribute the actual 
excavation of the fjords to glacial erosion. In a similar manner 
Reusch 63 for the Norwegian fjords and Andrews 64 for those of 
New Zealand, make a clear distinction between the role of faulting 
in determining lines of weakness favorable to rapid stream and 
glacial erosion, and the role of glaciers in giving to the fjords 
their present form and depth. 

In 1895 Shaler 65 , in discussing changes of sealevel, accepted 
the glacial origin of fjords and stated that since glaciers may cut 
their channels below the surface of the sea, the flooding of a 
glacial trough may be accomplished as the ice melts, without any 
sinking of the land or rising of the water level. This same view, 
that fjords do not indicate past changes of level, was adopted 



180 TERMINOLOGY AND CLASSIFICATION OF SHORES 



Plate XVIII. 




Photo by Underwood & Underwood. 

The Naero Fjord, Norway, a partially submerged glacial trough. 



SHORELINES OF SUBMERGENCE 181 

by Hubbard 66 in a brief review of the fjord problem which he 
published in 1901; by Daly 67 in his account of the Labrador 
fjords; and by Andrews 68 in discussing the fjords of New Zealand. 
It is further elaborated by Gilbert 69 in his report on glacial studies,, 
forming the third volume of the Harriman Alaska Series, where 
the reader will find a discussion of the physics of glacial erosion 
below sealevel. Marshall 70 in his " Geography of New Zealand," 
and Tarr 71 in his report on the " Physiography and Glacial 
Geology of the Yakutat Bay Region, Alaska " are among other 
students of fjords who attribute their excavation to ice erosion. 

Members of the non-glacialist group are by no means in agree- 
ment among themselves as to the origin of fjords. They agree 
on one thing only — that ice did not excavate these deeply sub- 
merged canyons. Some consider fjords the product of normal 
stream erosion followed by a partial submergence which per- 
mitted the valleys to be drowned. This was the view expressed 
by Dana 72 , who first emphasized the restriction of fjords to high 
latitudes but did not suggest for them a glacial origin. Upham 73 
definitely rejects the glacial explanation, and follows Dana in 
considering fjords as drowned normal river valleys. Brigham 74 
and Hull 75 seem to incline to the same view, the former speaking 
of " the common sense conclusion that they are river valleys 
made tidal by drowning"; but both recognize that fjords have 
been to some extent modified by glaciers. Hirt 76 in a review of 
" Das Fjord-Problem," Dinse 77 in a more elaborate study of 
" Die Fjordbildungen," and Grossman and Lomas 78 in a report 
on the Faroe Islands tend to assign to glaciers but a moderate 
role in modifying pre-existing valleys; while J. W. Tayler 79 and 
Fair child 80 definitely reject the glacial theory of fjord formation, 
Fairchild specifically invoking coastal subsidence to account 
for the fjord embayments. 

Among those students who admit that ice erosion played an 
essential part in fashioning fjord valleys, there are a number who 
either expressly require coastal subsidence, or else tacitly assume 
that subsidence is necessary for the drowning of the glacial 
troughs. Robert Brown 81 writing on the " Formation of Fjords " 
in 1869 and 1871, required the combined action of glacial erosion 
and coastal subsidence. The same view is supported by Rem- 
mers 82 in his " Untersuchungen der Fjorde an der Kuste von 
Maine," and by Guttner 83 in an essay on " Geographische 



182 TERMINOLOGY AND CLASSIFICATION OF SHORES 

Homologien an den Kusten " published in 1895. Those writers 
assuming the necessity of subsidence without specifically dis- 
cussing the point, include Penck 84 in his " Morphologie der 
Erdoberflache," de Lapparent 85 in his " Traite de Geologie," 
Gallois 86 in his account of " Les Andes de Patagonie," Le Conte 87 
in his " Elements of Geology," and Hobbs 88 in his " Earth 
Features and Their Meaning." 

Formerly many observers were inclined to regard every fjord 
as either a rift valley formed by the dropping down of a narrow 
strip of the earth's crust between two parallel faults, or as a 
gaping chasm opened along a single fault. This tectonic theory 
of the origin of fjords, once much in vogue as an explanation for 
all valleys, is now generally regarded as obsolete. Statements of 
the tectonic theory in which ice is credited with a very minor 
role in clearing out crushed and broken rock left in the fault 
cleft, or in the moderate widening of an open chasm, will be 
found in a short paper by Gurlt 89 , entitled " Uber die Entste- 
hungsweise der Fjorde," published in 1874, in Peschel's " Neue 
Probleme der vergleichenden Erdkunde als Versuch einer 
Morphologie der Erdoberflache " 90 , dated four years later; and 
in Kornerup's account of the fjords of southwest Greenland 91 . 
A more modern supporter of the tectonic origin of ' fjords is 
Steffen 92 in a short paper on " Der Baker-Fjord in West- 
Patagonien." But by far the most elaborate thesis in support 
of the tectonic theory is J. W. Gregory's recent book on " The 
Nature and Origin of Fjords " 93 . This serious attempt to re- 
habilitate a much-discredited theory of fjord origin contains 
extensive references to the literature of fjords, but frequently 
misinterprets the views held by the authors quoted. In a critical 
review of the book the present writer 94 has endeavored to show 
that Gregory's arguments are based upon a misconception of 
what the glacial theory of fjords implies, and upon an uncertain 
and variable interpretation of the tectonic theory. 

Readers who wish to follow the discussion of the fjord prob- 
lem further will be interested in an essay by Nordenskjold 95 
on " Topographisch-geologische Studien in Fjordgebieten " and 
in a shorter paper by Werth 96 entitled " Fjorde, Fjarde, und 
Fohrden." Both contain many references to the literature of 
the subject, and Werth's paper explains the differences between 
typical fjords, the allied forms in low rocky coasts like south- 



SHORELINES OF SUBMERGENCE 



183 



Plate XIX. 




Photo by Underwood & Underwood. 

Lake Loen, Norway, occupying a glacial trough and practically continuous 
with the upper part of Nord Fjord. Compare with similar topography 
shown on Plate XVIII. 



184 TERMINOLOGY AND CLASSIFICATION OF SHORES 

western Sweden sometimes called fiards (Plate XX), and the 
fohrden of the Baltic shores of Denmark and Schleswig-Hol- 
stein, similar to fiards but lacking their rocky shores. The 
relations of these three sub-types of fjords are also considered 
by Penck 97 , Dinse 98 , and Hubbard 99 . An early paper by Ratzel 100 
discusses at some length the essential characteristics of fjords. 

Without, at this time, entering into any elaborate discussion 
of the several theories of fjord formation, it may be said that the 
interpretation which would regard fjords as partially submerged 
river valleys fails to account on any rational basis for the re- 
striction of true fjords to glaciated high latitudes, for the 
identity in form between fjord- valleys and the glacial troughs 
of glaciated high altitudes, for the almost uniform violation of 
Play fair's law by tributary valleys which enter main fjords with 
discordant junctions, and for the occurrence of submerged fjord 
basins which, were the land to stand higher, would become lake 
basins not distinguishable from those of typical glacial troughs. 
Special pleading and strained reasoning have suggested a variety 
of possible explanations for each of these characteristic relation- 
ships, some of which might apply in one given instance, others 
in another. Glacial over-deepening of pre-existing river valleys 
alone offers a single explanation adequate to account at once for 
all of the specified relationships in all of the observed cases. 

The tectonic theory of fjords is based on a misunderstanding 
of the significance of the known occurrence of fault-lines in 
certain fjords, and of the rectangular pattern of other fjords, 
which suggests an intersecting fault pattern. There can be 
little doubt but that crushed zones along faults, and infaulted 
strips of weak rock, have often determined the position and 
pattern of fjord- valleys. It is, however, an error of reasoning 
to jump to the conclusion that faults make fjords. As already 
noted, the glacial theory of fjord origin fully recognizes the fact 
that the pre-glacial valleys later transformed into fjords were 
often excavated along ancient fault-lines. Stream erosion natu- 
ally took advantage of the weak belts determined by faulting, 
forming fault-line valleys; but not until ice occupied these pre- 
glacial stream valleys and profoundly changed their shape and 
their depth, were the forms which we called fjords produced. 
To prove the presence of a fault-line through a fjord is, therefore, 
to prove nothing as to the tectonic origin of the fjord. The 



SHORELINES OF SUBMERGENCE 



185 



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o 

o 

^3 



IHHBnHHHMnHB 



186 TERMINOLOGY AND CLASSIFICATION OF SHORES 

tectonic theory, moreover, affords no rational explanation of the 
restriction of fjords to high latitudes, nor of the identity in form 
between fjord valleys and unsubmerged glacial troughs, between 
fjord-basins and trough lake-basins. In the glacial theory alone 
do all of the phenomena cited, including the relation of fjords to 
faults, find a logical interpretation. 

It should be noted that the subsidence of the land, which was 
an essential element of the theory that fjords are drowned normal 
river valleys, has been specifically invoked or tacitly assumed by 
many of the supporters of the tectonic and glacial theories. 
Whatever may be said regarding the discarded tectonic theory, 
it is clearly an error of reasoning which would assume the neces- 
sity of land sinking in order to account for partial submergence 
of glacially over-deepened valleys. Glaciers in high latitudes 
reach the sea at the present time; and glaciers cannot cease to 
erode their channels until the ice is floated, which in turn cannot 
occur until the glacier has cut something like six-sevenths of its 
thickness below sealevel. Shaler was clearly right in stating 
that the over-deepened channel of such a glacier would be flooded 
by the sea as the ice melted, without any sinking of the land. It 
is important to remember, therefore, that there is no solid 
ground for the popular opinion that fjords are an indication of 
land subsidence. 

II. Shorelines of Emergence. — The typical shoreline of 
emergence is the coastal plain shoreline, resulting from the emer- 
gence of a submarine or sublacustrine plain. Whatever may 
have been the initial inequalities of a given sea-bottom or lake- 
bottom, deposition of sediment will in time obliterate them. The 
resultant smooth bottom is protected from the action of those 
subaerial agents of erosion which normally give to the lands 
their remarkable variety of relief. Waves and currents tend 
to reduce irregularities of the subaqueous surface, not to produce 
them. We should, therefore, expect that most shorelines of 
emergence would be coastal plain shorelines; and this indeed 
seems to be the case. 

It is conceivable that an irregular, dissected land mass might 
first be submerged, and then experience partial emergence before 
there was time for subaqueous processes to obliterate the ir- 
regularities. In such a case the shoreline would be classed as 
a shoreline of submergence, since all its chief characteristics are 



NEUTRAL SHORELINES 



187 



determined by the earlier major movement of submergence and 
not by the later minor emergence. This is the case with the 
extremely irregular shoreline of Maine, which is frequently cited 
as a type example of the shoreline of submergence, notwithstand- 
ing a late uplift of the coast of moderate amount. Similarly the 
coastal plain of southern New Jersey and the coastal plain of 
Texas afford good examples of shorelines of emergence, although 
a later slight submergence has resulted in moderate embayment 
of the inner shorelines behind the offshore bars. 

On theoretical grounds one might discuss other types of shore- 
lines of emergence, as, for example, the shoreline which would 
be formed if an original submarine volcano were raised partially 
above sealevel by the upwarping of the ocean floor. Such dis- 
cussion would not, however, materially add to our understanding 
of the principles of 
shoreline develop- 
ment, and may better 
be left to those who 
in the future encoun- 
ter examples of such 
shorelines meriting 
special description. 

III. Neutral Shore- 
lines. — While most 
of the world's shore- 
lines have resulted 
from submergence of 
land areas or emer- 
gence of subaqueous 
surfaces, there remain 
important groups of 
shorelines whose es- 
sential characteristics 
depend on causes in- 
dependent of either 
submergence or emer- 
gence. To this class of shorelines I propose to apply the term 
"neutral shorelines." Among others, the class will include the 
well-known (a) delta shorelines of variable form and extent. 
Where the current of a river's distributaries strongly predomi- 




Fig. 26. 



Mississippi Delta. A typical 
lobate delta. 



188 TERMINOLOGY AND CLASSIFICATION OF SHORES 



nate over shore currents and wave attack, the delta shoreline 
will be of the " lobate " type, as in the case of the Mississippi 
delta (Fig. 26). If shore currents or possibly wave erosion, or 
both, have a marked effect in shaping most of the accumulating 
delta deposit, but the river along one principal channel con- 
tinues to advance its mouth into the lake or sea, a " cuspate " 

delta shoreline like that of the 
Tiber (Fig. 27) will result. In 
case either shore current or wave 
attack sets a limit to delta growth, 
even at the mouths of distribu- 
taries, what I have termed an 
" arcuate " delta shoreline may 
be formed, of which type the 
Niger delta (Fig. 28) seems to fur- 
nish a good example. Interme- 
diate stages between these several 
types, or combinations of two or 
more types in a single delta, are 
frequently encountered. 

Closely related to delta shore- 
lines are (b) alluvial plain shore- 
lines, and (c) outwash plain shore- 
lines, formed where the broad 
alluvial slope at the base of a 
mountain range or the outwash 
plain in front of a glacier is built 
forward into a lake or the sea. 
On the landward side of such 
shorelines the topography is simi- 
lar in many respects to that bor- 
dering the coastal plain shoreline, 
and the same may be true of the immediate offshore zone. 
Farther seaward the slope would normally become steeper, like 
the frontal slope of a delta, (d) Volcano shorelines of more or 
less circular pattern are formed where an active volcano, pro- 
jecting above the water surface, builds its cone upward and out- 
ward by continued addition of ejected materials. 

A very important group of neutral shorelines consists of (e) 
coral reef shorelines, formed when coral polyps build reefs upward 




Fig. 27. — Delta of the Tiber. 
A cuspate delta. 



NEUTRAL SHORELINES 



189 




Fig. 28. 



Niger Delta. The type of 
arcuate delta. 



from a submarine floor or outward from the margins of any land 
area. Whatever the influence which past subsidence of the sea- 
bottom or elevation of the water surface may have exerted upon 
the particular forms assumed by coral reefs, does not affect the 
fact that the present shorelines of the reefs owe their existence 
to agencies which operate independently of such changes of 
level. The reef shore- 
lines do not mark the 
contact of the water 
surface with pre-ex- 
isting land areas or 
sea-bottoms, but with 
newly made land in 
process of formation 
at the present level. 
It would be out of 
place to enter here 
into a discussion of 
the much mooted 
coral reef problem. 
Those desiring to pursue this subject should consult the writ- 
ings of Davis 101 , and Daly 102 , wherein discussions of the earlier 
work of Darwin, Dana, Murray and Agassiz will be found, to- 
gether with copious references to the extensive literature pub- 
lished by other investigators of the problem. Vaughan 103 briefly 
discusses different theories of coral reef origin in a short paper 
published in 1916. 

Another important group of shorelines belonging to the neutral 
class consists of (/) fault shorelines. The best discussion of this 
type of shorelines is contained in an excellent essay by Cotton, 104 
to which we will recur on a later page. When the block on the 
downthrow side of a fault is so far depressed as to permit the 
waters of sea or lake to rest against the fault scarp, we have the 
typical fault shoreline (Fig. 29). Cotton describes shorelines 
of this type from near Wellington, and from other parts of New 
Zealand. 

Earlier geological literature is full of references to shorelines 
or coasts supposed to result from faulting. Practically every 
irregular rocky coast has been explained as the ragged, broken 
edge of a land mass bordering a down-dropped segment of the 



190 TERMINOLOGY AND CLASSIFICATION OF SHORES 



earth's crust. Descriptions of these coasts abound in such ex- 
pressions as " fractured table-land bordering a foundered area," 
11 the foundering of the adjacent ocean bed," " fractured margins 
of horsts," " the collapse of the basin of the Adriatic," and " shat- 
tered margin of the continent." Supported by the authority 
of men like Suess, the interpretation of irregular coasts as the 




Fig. 29. — Initial stage of a fault shoreline. (Modified after Cotton.) 

ragged edge of the land left standing when the adjacent area 
foundered beneath the sea, gained a currency, especially among 
German students 105 , out of all proportion to its merits. It is now 
widely recognized that most, if not all, of these extremely ir- 
regular shores are better explained as shorelines of submergence, 
unrelated to faulting. Yet not a few writers of today, including 
occasionally a trained physiographer, show the influence of Suess' 
teaching by invoking the " shattering and foundering " theory for 
coasts like those of Greece, Dalmatia, and Norway. Fault 
shorelines exist; but so far as described by critical observers on 
the basis of competent evidence, they do not exhibit the irregular 
pattern of the coasts just mentioned. Shorelines of submergence, 
on the contrary, either of the ria or fjord type, show precisely 
those characteristics well displayed along the three coasts in 
question. 

IV. Compound Shorelines are those which are prominently 
characterized by phenomena normally characteristic of at least 
two of the preceding classes. It frequently happens, for example, 
that oscillations in the level of land or sea leave a shoreline with 
a variety of features, some of which resulted from submergence, 
others from emergence. This is the case with the shoreline of 



COMPOUND SHORELINES 



191 



North Carolina (Fig. 30), 
which combines the drowned 
valleys of a shoreline of sub- 
mergence with the offshore 
bar of a shoreline of emer- 
gence in such manner that 
it is difficult to decide which 
set of features is more promi- 
nent. We can therefore most 
properly speak of it as a com- 
pound shoreline. 

In the formation of fault 
shorelines it may well happen 
that the block on the up- 
throw side of the fault is 
itself sufficiently depressed to 
permit drowning of the more 
deeply cut main valleys (Fig. 
31). Such cases are reported 
from New Zealand by Cot- 
ton 106 , and afford a very 




Fig. 30. — Coast of North Carolina, 
showing one type of compound 
shoreline. 



striking example of compound shorelines. 

The term compound shoreline should be employed only when 
there is a very marked development of the features character- 
istic of two or more of the simpler classes of shorelines. Such 




Fig. 31. — Compound shoreline due to faulting and partial submergence of 

upthrow block. 



192 TERMINOLOGY AND CLASSIFICATION OF SHORES 

a shoreline as that of eastern Florida would be classed as a 
shoreline of emergence, notwithstanding the mild indications 
of submergence presented by the drowned valleys. 

Stages of Shoreline Development. — The character of any 
shoreline depends, in the last instance, on the amount of work 
accomplished by marine agents upon the land against which the 
water surface comes to rest; or, in other words, upon the stage of 
shoreline development. Shorelines of submergence, shorelines of 
emergence, neutral shorelines, and compound shorelines of all 
varieties must therefore be further subdivided into groups accord- 
ing as they are in the initial, young, mature, or old stage of de- 
velopment, each group having its own peculiar characteristics. 
What these characteristics are will appear at some length in the 
following chapters. 

RESUME 

We have outlined a terminology for the broader topographic 
features which characterize the margins of the land and sea. 
These features include four zones, known as the coast, shore, 
shore-face and offshore; three erosion forms, the cliff, bench, and 
abrasion platform; and three deposits called the beach, veneer, 
and continental terrace. All of these features are not invariably 
present, for we have already observed that the beach may be 
lacking, and it will appear in later chapters that one or more 
of the other features mentioned may fail to be developed in 
special cases. Shorelines have been classified into four main 
groups: shorelines of submergence, shorelines of emergence, 
neutral shorelines, and compound shorelines. The subdivisions 
of each class have been briefly considered, and some examples 
cited. We are now prepared to study the development of 
shores, by considering first the development of the shore profile, 
after which the shoreline itself will be treated. 



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60. Haast, J. von. Notes on the Causes which have led to the Excava- 

tion of Deep Lake-basins in Hard Rocks in the Southern Alps of New 
Zealand. Quart. Jour. Geol. Soc, XXI, 130-132, 1865. 

61. Helland, Amund. Die Glaciale Bildung der Fjorde und Alpenseen in 

Norwegen. Annalen Physik Chemie, CXLVI, 538-562, 1872. 



196 TERMINOLOGY AND CLASSIFICATION OF SHORES 

Helland, Amund. On the Ice-fjords of North Greenland and on the 
Formation of Fjords, Lakes, and Cirques in Norway and Greenland. 
Quart. Journ. Geol. Soc, XXIII, 142-176, 1877. 

- 62. Brogger, W. C. tlber die Bildungsgeschichte des Kristianiafjords: 

Ein Beitrag zum Verstandniss der Fjord-und Seebildung in Skandi- 
navien Nyt. Mag. Nat. XXX, 99-231, 1886. 
63. Reusch, H. Some Contributions towards an Understanding of the 
Manner in which the Valleys and Mountains of Norway were Formed. 
Norges Geol. Undersog, Aarbog for 1900. 239-263, 1901. 
.-,- - 64. Andrews, E. C. Erosion and its Significance. Jour. Proc. Roy. Soc. 
N. S. Wales. XLV, 115-136, 1911. 

- 65. Shaler, N. S. Evidences as to Changes of Sealevel. Geol. Soc. Amer., 

Bull., VI, 141-166, 1895. 

- 66. Hubbard, G. D. Fiords. Bull. Amer. Geogr. Soc. XXXIII, 406, 

1901. 
67. Daly, R. A. The Geology of the Northeast Coast of Labrador, Bull. 
Mus. Comp. Zool. XXXVIII, 211, 1902. 

- - 68. Andrews, E. C. The Ice-Flood Hypothesis of the New Zealand Sound 
Basins. Jour, of Geol., XIV, 22-54, 1906. 
— Andrews, E. C. Corrosion by Gravity Streams, with Applications of 
the Ice-Flood Hypothesis. Jour, and Proc. R. Soc. N. S. Wales. 
XLIII, 204-330, 1909. 

». 69. Gilbert, G. K. Glaciers and Glaciation. Harriman Alaska Expedi- 
tion. Ill, pp. 159, 162-163, 210^218, 1904. 

70. Marshall, P. The Geography of New Zealand. 401 pp., 1905. 

71. Tarr, R. S. The Yakutat Bay Region, Alaska, Physiography and 

Glacial Geology. Professional Paper 64, U. S. Geol. Surv. 183 pp., 
1909. 
_ 72. Dana, J. D. Geology, U. S. Exploring Expedition during the years 
1838 to 1842 under the Command of Charles Wilkes. X, 676, 1849. 
Dana, J. D. Manual of Geology, p. 543, Philadelphia, 1863. 

73. Upham, Warren. The Fiords and Great Lake Basins of North America 

Considered as Evidence of Preglacial Continental Elevation and of 
Depression during the Glacial Period. Bull. Geol. Soc. Amer., I, 
563-567, 1890. 
Upham, Warren. Fiords and Hanging Valleys. Amer. Geol. XXXV, 
312-315, 1905. 

74. Brigham, A. P. The Fiords of Norway. Bull. Amer. Geog. Soc, 

XXXVIII, 337-348, 1906. 

75. Hull, Edward. The Physical History of the Norwegian Fjords. 

Geol. Mag. Dec. V, Vol. X, 9-14, 1916. 

76. Hirt, Otto. Das Fjord-Problem. Jahresb. des Konigl. Gymnasi- 

ums zu Soran. 12 pp., 1888. 

77. Dinse, P. Die Fjordbildungen. Ein Beitrag zur Morphographie der 

Kusten. Zeit. der Ges. fur Erdkunde zu Berlin. XXIX, 189-259, 
1894. 

78. Grossman, K. and Lomas, J. On the Glaciation of the Faroe Islands, 

Glacialists' Mag. Ill, 1-15, 1895. 



REFERENCES 197 

79. Tayler, J. W. On Greenland Fiords and Glaciers. Proc. Roy. Geog. 

Soc. XIV, 156-158, 1870. 

80. Fairchild, H. L. Ice Erosion Theory a Fallacy. Bull. Geol. Soc. 

Amer. XVI, 13-74, 1905. 

81. Brown, Robert. On the Formation of Fjords, Canons, Benches, 

Prairies, and Intermittent Rivers. Jour. Royal. Geog. Soc. XXXIX, 
121-131, 1869. 
Brown, Robert. Remarks on the Formation of Fjords and Canons. 
Jour. Royal Geog. Soc. XLI, 348-360, 1871. 

82. Remmers, Otto. Untersuchungen der Fjorde an der Kuste von 

Maine. 63 pp., Leipzig, 1891. 

83. Guttner, Paul. Geographische Homologien an den Kiisten mit be- 

sonderer Beriicksichtigung der Schwemmlandkiisten. 59 pp., Leip- 
zig, 1895. 

84. Penck, A. Morphologie der Erdoberflache. II, 696 pp., Stuttgart, 

1894. 

85. Laparrent, A. de. Traite de Geologie; Phenomenes Actuels. 591 

pp., Paris, 1900. 

- 86. Gallois, L. Les Andes de Patagonie. Annales de Geographic X, 

232-259, 1901. 

87. Le Conte, Joseph. Elements of Geology. 5th Edit. 667 pp., New 
£ York, 1904. 

88. Hobbs, W. H. Earth Features and their Meaning. 506 pp., New 

York, 1912. 

89. Gurlt, F. A. Uber die Enstehungsweise der Fjorde. Sitz. Nieder- 

rheinischen Ges. Natur- und Heilkunde. XXXI, 143-150, 1874. 

90. Peschel, O. Neue Probleme der Vergleichenden Erdkunde als Versuch 

einer Morphologie der Erdoberflache. 215 pp., Leipzig, 1878. " 

91. Kornerup, A. Geologiske Iagttagelser fra Vestkysten af Gronland 

(66° 55'-68° 15'' N. B.) Meddel, om. Gronl. II, 149-194, 1881. 
i 92. Steffen, Hans. Der Baker-Fiord in West-Patagonien. Pet. Geog. 
Mitt. L, 140-144, 1904. 

93. Gregory, J. W. The Nature and Origin of Fjords. 542 pp., London, 

1913. 

94. Johnson, Douglas W. The Nature and Origin of Fiords. Science, 

N. S. XLI, 537-543, 1915. 
' 95. Nordenskjold, Otto. Topographisch-geologische Studien in Fjord- 

gebieten. Bull. Geol. Inst. Univ. Upsala. IV, 157-226, 1900. 
; 96. Werth, Emil. "Fjorde, Fjarde, und Fohrden, Zeit. fur Gletscherkunde . 

Ill, 346-358, 1909. 

97. Penck, A. Morphologie der Erdoberflache. II, 696 pp., Stuttgart, 1894. 

98. Dinse, P. Die Fjordbildungen. Ein Beitrag zur Morphographie der 

Kiisten. Zeit. der Ges. fur Erdkunde zu Berlin. XXIX, 189-259, 
1894. 

- 99. Hubbard, G. D. Fiords. Bull. Amer. Geog. Soc. XXXIII, 330-337, 

401-408, 1901. 
100. Ratzel, Fr. Uber Fjordbildungen an Binnenseen; nebst Allgemeinen 
Bemerkungen uber die Begriffe Fjord und Fjordstrasse und die 



198 TERMINOLOGY AND CLASSIFICATION OF SHORES 

Nord-Amerikanischen Kiistenf jorde. Pet. Geog. Mitt. XXVI, 387- 
396, 1880. 
— 101. Davis, W. M. Dana's Confirmation of Darwin's Theory of Coral Reefs. 
Amer. Jour. Sci. XXXV, 173-188, 1913. 
.-.. Davis, W. M. Home Study of Coral Reefs. Bull. Amer. Geogr. Soc. 
XLVI. 561-577, 641-654, 721-739, 1914. 
Davis, W. M. Shaler Memorial Study of Coral Reefs. Amer. Jour. 

Sci. XL, 223-271, 1915. 
Davis, W. M. Problems Associated with the Origin of Coral Reefs. 
Scientific Monthly. II, 313-333, 479-501, 557-572, 1916. 

102. Daly, R. A. Pleistocene Glaciation and the Coral Reef Problem. 

Amer. Jour. Sci. XXX, 297-308, 1910. 
-Daly, R. A. The Glacial-control Theory of Coral Reefs. Proc. Amer. 
Acad. Arts and Sciences. LI, 158-251, 1915. 
Daly, R. A. Problems of the Pacific Islands. Amer. Jour. Sci., XLI, 
153-186, 1916. 

103. Vaughan, T. Wayland. Present Status of the Investigations of the 

Origin of Barrier Coral Reefs. Amer. Jour. Sci. XLI, 131-135, 1916. 

104. Cotton, C. A. Fault Coasts in New Zealand. The Geographical 

Review. I, 20-47, 1916. 

105. Fischer, Theobald. Zur Entwickelungs-Geschichte der Ktisten. Pet. 

Geogr. Mitt. XXXI, 409-420, 1885. 
Cold, Conrad. Kiisten-Veranderungen im Archipel. 67 pp., Mar- 
burg, 1886. 
*_ Hentzschel, Otto. Die Hauptkiistentypen des Mittelmeers. 61 pp., 
Leipzig, 1903. 

106. Cotton, C. A. Fault Coasts in New Zealand. The Geographical 

Review. I, 20-47, 1916. 



CHAPTER V 

DEVELOPMENT OF THE SHORE PROFILE 

SHORELINES OF SUBMERGENCE 

Advance Summary. — In the development of any shoreline there 
are significant and systematic changes both in the profile and in 
the plan of the land margin. These changes take place in orderly 
sequence, and may best be described as the young, mature, and 
old stages of a cycle of shore development. We shall find, how- 
ever, that the stages of shore profile development and the stages 
of shoreline development do not always keep pace with each 
other. A mature shoreline may have the shore profile of some 
of its parts still in the stage of youth; and it very commonly 
happens that a young shoreline has many points where the 
shore profile is mature. It will be desirable, therefore, to discuss 
the cycle of the shore profile first, and later to consider the cycle 
of the shoreline as a whole. In the present chapter the terms 
youth, maturity, and old age refer to stages of profile development 
only. The significant features of the profile involve all four of 
the zones adjacent to the shoreline, and when reference is made 
in the following paragraphs to the shore profile, it should be under- 
stood to include not only the shore proper, but the shoreface, 
offshore, and coast as well. 

It has been deemed advisable to discuss first, and somewhat 
at length, profiles characteristic of the youth, maturity and old 
age of shorelines of submergence. Special attention is given to 
beach profiles and to their constantly shifting forms, matters of 
vital importance in many . problems of marine engineering. A 
study of the ultimate stage of the shore profile leads logically to 
a consideration of the theory of marine planation. This theory 
is discussed fully and arguments presented to support the opinion 
that it merits a greater measure of confidence than most stu- 
dents of landforms are accustomed to accord it. The marine 
and fluvial cycles of erosion are correlated, their essential inde- 
pendence is emphasized, and their relative importance compared. 

199 



200 



DEVELOPMENT OF THE SHORE PROFILE 




INITIAL STAGE 



201 



In the final sections of the chapter the fea- 
tures peculiar to profiles across shorelines of 
emergence, neutral shorelines, and compound 
shorelines are given special treatment. 

Initial Stage. — The initial profile at right- 
angles to a shoreline of submergence nor- 
mally indicates comparatively steep slopes 
descending rather abruptly into the water 
(a 1 , Fig. 32). This is because submergence 
ordinarily permits the water level to come 
to rest against the hill-sides of the former 
land area. It is true that certain excep- 
tions must be recognized. If the land area 
had been reduced to a peneplane surface 
before submergence, or if the form sub- 
merged were a young, undissected alluvial 
plain or other similar surface, then the initial 
profile will resemble that normally char- 
acteristic of a shoreline of emergence, and 
the history of development will be that 
appropriate for such a profile. Here we 
deal only with the more usual case, in which 
submergence permits the sea to come to 
rest against the irregular and comparatively 
pronounced hill slopes of a submature, 
mature, or late mature land mass. 

Waves will at once attack the land at 
this new level, their vertical zone of activity 
extending from a short distance below sea- 
level to a short distance above; because, as 
we have already seen, the forward dashing 
crests of storm waves rise some feet above 
mean water level, while the vigor of wave 
activity dies out very rapidly below it. 
Although the waves do carry on a milder 
erosive activity at greater depths, the attack 
near the surface level is so much more 
vigorous that it is fair to liken the sea to a 
horizontal saw which cuts laterally into the 
land, the blade of the saw having a thick- 




202 



DEVELOPMENT OF THE SHORE PROFILE 




YOUNG STAGE 203 

ness which extends from a few feet above to a few feet below 
sea level and being armed with breaking waves for teeth. Wave 
erosion soon cuts a notch in the edge of the sloping land, and thus 
destroys the initial profile. The coarse debris resulting from this 
erosion descends the underwater slope until it comes to rest as 
a submarine talus, where the water is deep enough to render 
wave agitation mild and the slope is gentle enough to require 
much agitation for the ready removal of coarse material. 

Young Stage. — Continued wave erosion soon pushes the notch 
so far into the land that the unsupported overhanging rock falls 
down under the influence of the forces of weathering, including 
the action of gravity and rain wash on the face of the slope. 
This produces the wave-cut cliff (6 3 ), in front of which is the wave- 
cut rock terrace called the bench (b 2 ). The eroded debris will 
be added to the submarine talus (6 1 ) if the shoreface slope is 
steep enough and the water deep enough, except such part as is 
ground sufficiently fine to be widely distributed over the sea- 
bottom far offshore. If the water is shallow or the slope gentle, 
a shoreface terrace may be formed at this time. 

In the cycle of stream development, the longitudinal profile 
of the young stream is characterized by irregularities which had 
their origin in the initial roughness of the land over which the 
stream flowed, or in the unequal erosion of alternate belts of re- 
sistant and non-resistant rock. Material eroded from parts of 
the profile exposed to vigorous cutting are deposited in the de- 
pressions of the profile where deep water is found. So also in the 
young shore profile we have irregularities due to the initial rough- 
ness of the submerged land mass, as well as irregularities in both 
cliff and bench (6 3 , b 2 ) due to unequal resistance of the rock masses 
which are being eroded; and the material torn from the zones 
exposed to attack are deposited in the depressions of the profile 
where deeper and quieter waters occur. 

As Davis 1 has shown, we may press this analogy even further 
with profit. In the typical young stream the water movement is 
vigorous because the initial slope of the land is comparatively 
steep, permitting a high velocity; transporting and eroding power 
are both great, but the transporting power is far more than 
sufficient to remove all the products of direct erosion. As the 
stream cuts downward the valley walls are undermined, and 
weathering causes the higher portions to descend into the stream 



204 DEVELOPMENT OF THE SHORE PROFILE 

channel. But even the addition of these products of weathering 
does not over-tax the transporting power of the stream, and all 
the debris is swept down-valley to be deposited in quieter water 
below. The quantity of the products of weathering is not large, 
for the reason that since the stream has not yet cut deeply into 
the land, the valley walls are not high and therefore do not ex- 
pose any considerable area to the forces of weathering. Because 
the rate at which the valley walls retreat, due to the forces of 
weathering, is not great as compared with the rate of valley 
deepening due to stream erosion, the slope of the valley walls is 
steep and may be vertical or even over-hanging in places. 

Turning our attention to the shore, we observe precisely anal- 
ogous conditions. Along the typical young shoreline of sub- 
mergence the wave action is vigorous, because the initial slope of 
the coast is comparatively steep, permitting large waves to reach 
the land; transporting power and eroding power are both great, 
but the transporting power is far more than sufficient to remove 
from the base of the cliff all the products of direct erosion. As 
the waves cut inward the cliff is undermined, and weathering 
causes the higher portions to descend upon the marine bench. 
But even the addition of these products of weathering does not 
over-tax the transporting power of the wave currents, and all the 
debris is swept seaward to be deposited in the quieter deep water. 
The quantity of the products of weathering is not large, for the 
reason that since the waves have not yet cut far into the land, 
the marine cliff is not high and therefore does not expose any 
considerable area to the forces of weathering. Because the rate 
at which the face of the cliff retreats, due to the forces of weather- 
ing, is not great as compared with the rate of backward cutting 
due to wave erosion, the slope of the cliff face is steep, and may 
be vertical or even over-hanging in places. 

A later stage of the youth of the shore profile shows some sig- 
nificant changes. As the waves cut farther into the land their 
power decreases because they must traverse greater and greater 
stretches of shallow water over the broadening marine bench; 
just as the stream which cuts deeper into a land mass suffers loss 
of erosive power because the water must flow more sluggishly on 
gentler and gentler gradients. But the loss of wave power 
comes at a time when the work to be done is increasing, for the 
increased height of the cliff enables the forces of weathering to 



YOUNG STAGE 



205 




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206 DEVELOPMENT OF THE SHORE PROFILE 

cast a larger amount of debris upon the marine bench below; just 
as the higher valley walls of a deepening stream shed more waste 
into the channel at the very time the stream current is becoming 
more sluggish because of the decreased gradient. In both cases 
the work to be done increases as the power to do work decreases. 
A larger proportion of the weakening wave power must be con- 
sumed in transporting the increased amount of debris to deep 
water and in grinding the debris finer during the process of 
transportation, with the result that the base of the cliff is less 
and less vigorously pushed inland; just as a larger proportion of 
the weakening stream power must be used up in transporting 
the larger volumes of waste down-valley with the result that 
valley deepening is still further diminished. In the case of wave 
action, weathering now has the opportunity to wear back the 
marine cliff to a more gentle slope (c 3 ), which corresponds with 
the more gentle slopes of the valley walls in the similar stage 
of stream development. 

Other important changes remain to be noted. During the 
appreciable length of time required for the pushing back of the 
cliff, the upland surface has been weathered and eroded to a 
lower level (c 4 ). Weathering of the cliff face goes on rapidly 
enough to keep pace with the enfeebled wave cutting at the base 
of the cliff, so that there is no longer a prominent notch at the 
level of wave erosion. The accumulation of the debris swept 
seaward from the marine bench by wave and possibly other 
currents has resulted in the formation of a shoreface terrace (c 1 ) 
whose top surface is delicately adjusted to continue the slight 
seaward inclination of the marine bench (c 2 ). 

Still more important is the fact that the marine bench main- 
tains its seaward inclination, and is therefore lower at its outer 
margin than it was at that same locality in an earlier stage of 
development. Thus the bench at c 2 has been lowered from the 
position b 2 . There should be no difficulty in understanding this 
important change, and its causes and consequences. Waves 
continue to traverse the marine bench, and as the depth of the 
bench is not yet great enough to place it beyond the reach of 
wave action, it must suffer some erosion. The very fact that 
waves are weakened as they cross the bench toward the cliff 
proves that they have lost energy by expending it on the bottom. 
The debris weathered from the face of the cliff and eroded from 



YOUNG STAGE 



207 




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208 DEVELOPMENT OF THE SHORE PROFILE 

its base is dragged across the marine bench by wave currents, 
possibly aided by other currents, to be built into the shoreface 
terrace or moved into deeper water; and the long-continued 
action of this " marine sandpaper " must grind the surface of the 
bench ever lower and lower. As the outer part of the bench has 
been made longest and therefore exposed to continuous abrasion 
for the longest time, it is worn lower than the parts further land- 
ward. Thus the bench keeps its seaward inclination. 

The effects of the seaward inclination of the marine bench are 
all-important. We have seen that waves tend to break when the 
depth of the water equals the height of the wave; hence the 
deeper the water the larger the waves which can traverse it. 
Progressive lowering of the marine bench therefore means the 
continuous admission of large waves farther and farther across 
its surface. Were it not for this lowering, a shallow, horizontal 
bench would greatly reduce the size and power of the waves 
which reached the cliff. While this would not completely stop 
cliff erosion, as has sometimes been assumed, it would enormously 
retard it. The seaward inclination of the bench greatly facili- 
tates the removal of debris into deep water; for as we found from 
our study of wave action, if oscillatory waves produce equal im- 
pulses alternately landward and seaward, debris on an inclined 
sea-bottom must travel down the slope, whereas on a horizontal 
bottom it might remain in one place indefinitely. Effective 
removal of debris prevents it from protecting the cliff, and per- 
mits the waves to devote a greater proportion of their energy 
to cliff erosion. Thus in a second way the progressive lowering 
of the marine bench in such manner as to produce an inclined 
surface, greatly facilitates the recession of the shoreline under 
wave attack. A third important effect of the inclined bench is 
to raise the level of effective wave attack at the base of the cliff. 
We have observed in preceding chapters that winds blowing 
toward a steep coast with deep water offshore do not raise the 
water level appreciably, but that where the water is shallow its 
entire mass may receive a landward motion and thus pile up 
against the shore; that both oscillatory waves and waves of 
translation coming onshore raise the water level, waves of trans- 
lation most effectively; that oscillatory waves change to waves 
of translation on a gradually shelving bottom; and finally, 
that tidal and other currents moving in upon such an inclined 



YOUNG STAGE 



209 




■8 



o 



5E 



210 DEVELOPMENT OF THE SHORE PROFILE 

slope raise the water level more effectively than when they im- 
pinge upon a steep slope which descends rapidly to deep water. 
All of these factors co-operate to raise the level of wave attack, 
especially during storms, to a slightly higher position as the 
shoreline is pushed inland. On the other hand, the development 
of strong waves of translation on the shallowing bottom during 
storms may move debris landward temporarily, thereby delaying 
its removal from the marine bench into deep water, and so re- 
tarding cliff recession for a time. 

The notch at the base of the marine cliff is a measure of the 
ratio between wave erosion and weathering (including the ac- 
tion of gravity). When wave erosion is much the more vigorous, 
a pronounced notch occurs; when erosion exceeds weathering 
but slightly, the notch is only faintly developed, and if weathering 
is able to keep pace with erosion there will be no notch. Un- 
consolidated materials are quickly pulled down upon the marine 
bench by the action of gravity, which may be regarded as a very 
important element of weathering, since it is most efficient in 
promoting the disintegration of rock masses. As a result, ero- 
sion cannot gain on weathering sufficiently to produce a notch in 
sand cliffs and other unconsolidated material, even in the earliest 
stages of cliff erosion; whereas rocky coasts may possess good 
notches in early youth, faint notches in late youth, and none in 
maturity when weathering and erosion are delicately balanced. 

On tidal shores, especially where the range of the tides is great, 
account must be taken of the varying water level. In the initial 
stage the vertical extent of the notch may be increased because of 
wave erosion throughout the whole extent of the tidal range. 
But early in youth it will be found that the notch is developed 
at the high tide level. Larger and more vigorous waves reach 
the coast in the deeper water of high tide, and the cliff is pushed 
in more vigorously at that higher level. The waves at low tide 
are left to expend their force on the shelving marine bench, and 
thus to assist in deepening its seaward portion. The general 
relations of the different topographic elements along the shore 
are not greatly different from those which would obtain if the 
high tide level were the mean water level of a tideless sea. Some 
minor differences will be noted as occasion demands. 

Mature Stage. — The essential feature of maturity in the 
development of the shore profile is a condition of approximate 



MATURE STAGE 



211 



equilibrium between erosion, weathering, and transportation. 
In other words, the profile of maturity is, as in the case of the 
mature stream, a profile of equilibrium 2 . During youth the 
power of the waves to do work is far in excess of the work to be 
done. But as the development progresses the work to be done 
constantly increases, while the power to do work ever diminishes. 
There must come a time when the two are nicely balanced and 
equilibrium is established. This time ushers in the stage of 
maturity. 

The essential nature of the shore profile of equilibrium may be 
better appreciated from an inspection of the accompanying 
diagram (Fig. 33). Where the cliff profile is steep (c) and much 
debris is shed into the water, the waves require a comparatively 
steep subaqueous slope in order that with the effective aid of 
gravity they may 3 be able to remove the large amount of debris 




Fig. 33. — Successive profiles of equilibrium on a retrograding shore. 



offered to them. With cliffs of progressively decreasing steepness 
(c' and c"), more gently inclined subaqueous slopes will permit 
that nice balance between the amount of work required to re- 
move the diminished quantity of debris and the ability of the 
waves to do removal work, which we call " equilibrium." The 
subaqueous profile is steepest near the land where the debris is 
coarsest and most abundant; and progressively more gentle 
farther seaward where the debris has been ground finer and re- 
duced in volume by the removal of part in suspension. At every 
point the slope is precisely of the steepness required to enable the 
amount of wave energy there developed to dispose of the volume 
and size of debris there in transit. Examples of actual profiles 
of equilibrium are shown in Figure 34. 

Let us imagine that the profile d l -d? (Fig. 35) is the shore pro- 
file of equilibrium, and verify the condition of equilibrium by 



212 



DEVELOPMENT OF THE SHORE PROFILE 



noting the consequences which must arise if we disturb any part 
of that profile. By assumption the erosion at the base of the 
cliff is just sufficient to supply the amount of debris which, added 
to the material contributed by the weathering of the cliff face, 
will provide the wave currents with the exact amount of ma- 
terial they can transport across the marine bench and shoreface 



Miles 



^^^ 




s ^r~*~-rt-- — ?. - . 


... -- • • 


. 


• • X 


West Coast Madagascar Lat. S. 18° 53' to 19° 03' \ 




\z 




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n 



20 Miles 
Fathoms 

10 
20 
30 
40 
50 



\ 

\ 




u 
10 

20 

30 

r 


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• 


Southeast Coast Madagascar 

Between C.Itanovalona and Galleon Bay 


• J 
Lat. S. 25 o 05' 


50 



Fathoms 



Fig. 34. — Profiles of equilibrium off the Madagascar coast as plotted from 
charts by Barrell. Note the striking difference between the profile of 
the protected west coast and that of the exposed southeast coast. 



terrace to the front slope of the latter. Now, if we imagine 
the cliff (d 3 ) to weather more rapidly for any cause, this will 
mean an added accumulation of debris at the base of the cliff. 
The waves will have more material to transport and therefore 
less energy left to expend in erosion. Hence the base of the cliff 
is pushed back less rapidly than normally. But since the top 
of the cliff has weathered back more rapidly than usual, the 
ultimate result is a gentler slope for the cliff face. On the gentler 
slope weathering proceeds less rapidly than formerly, until the 
waves get rid of their excess burden and renew their erosion at 
the base of the cliff, thereby steepening it until weathering is 
once more normally adjusted to the other forces and equilibrium 



MATURE STAGE 



213 



is re-established. In a similar manner, if 
we disturb the equilibrium by increasing 
the wave erosion, this will mean more 
eroded material and products of weathering 
to be transported, wave currents will be 
overburdened, debris will accumulate un- 
duly on the marine bench, thereby shallow- 
ing the water and decreasing the size of the 
waves which can reach the cliff base, thus 
reducing erosion until equilibrium is again 
restored. Increase of transporting power 
would sweep the marine bench clean and 
allow waves to deepen it more effectively, 
thereby admitting larger waves to the cliff 
base to produce greater erosion, and so in- 
creasing the material to be moved until the 
transporting power of the waves was again 
balanced by the amount of material requir- 
ing removal. 

As in a mature river the equilibrium is 
never absolutely perfect, but rather an 
ideal condition which the stream ever 
strives to attain and does succeed in ap- 
proximating very closely; so at the shore, 
where the variation in wave attack is far 
more irregular than stream volume and 
velocity, the equilibrium of maturity is only 
approximate. Each set of waves endeavors 
to establish a profile of equilibrium suited 
to its own needs, but seldom succeeds be- 
fore another set of waves begins working 
toward a somewhat different profile. Fortu- 
nately, the small waves work so slowly as 
to effect no profound changes between times 
of vigorous wave action, while the attack 
of storm waves at a given point is sufficiently 
similar at different times to produce similar 
effects. There is, therefore, a certain char- 
acteristic profile of equilibrium for a given 
locality, notwithstanding the fact that 



214 DEVELOPMENT OF THE SHORE PROFILE 

minor variations in the forces there at work will produce local 
changes which tend to confuse the student of shore forms. Let 
us first note the broader features of the mature profile, and then 
consider some of the more variable minor features. 

In Figure 35 the profile d l -d A is that of maturity. Comparing 
it with c 1 -^, the profile of late youth, we note certain significant 
differences. The cliff d 3 has weathered back to a more gentle slope 
than in c 3 , because wave attack is more feeble when the waves 
must traverse a broader marine bench which is encumbered, as 
we shall see, by more or less debris. As erosion carries the cliff 
farther and farther inland it will from time to time occupy posi- 
tions on the landward-sloping sides of hills, in which positions the 
cliff decreases in height as it advances into the land (Plate VII) . 
The presence of such cliffs of decreasing altitude along a coast 
implies considerable wave erosion in the past. The upland (d 4 ) 
has worn down to a lower level during the time required for 
the cliff to retreat from c 3 to d z . As should be expected, the 
marine bench has likewise been worn lower at the same time that 
it has been extended inland; but it should be observed that al- 
though the cliff retreated twice as far from c 3 to d 3 as from ¥ to c 3 , 
the outer part of the marine bench has not been lowered in pro- 
portion. This is because the waves act more feebly with in- 
creasing depth, and because the bench is more protected by debris 
than formerly. In consequence of the rapid decrease in wave 
power with increase in depth, the shoreward portion of the bench 
has a steeper slope than the portion in deeper water; or, in other 
words, the profile of the bench is faintly concave upward. A 
notable extension of the shoreface terrace (d l ) is apparent, the 
front of the terrace being convex upward. The compound pro- 
file of the bench and shoreface terrace combined is therefore 
roughly sigmoid, faintly concave upward near the landward end 
and convex at the seaward end. 

The most important feature of maturity is the accumulation 
of debris on the marine bench to form a beach. During youth 
the vigorous wave action sweeps the products of weathering and 
erosion into deep water so rapidly that there may be no conspic- 
uous deposits of waste on the bench most of the time. In matur- 
ity, however, the journey from the base of the cliif to deep water 
is so long, and wave action over much of the distance is so 
moderate, that any given moment may witness a considerable 



MATURE STAGE 215 

quantity of debris in transit across the bench. Under normal 
conditions this material is not of appreciable depth, and its inter- 
mittent seaward movement serves to reduce the size of its com- 
ponent parts and to lower the level of the bench, by friction 
amongst the particles themselves and upon the bench surface. 
It is this beach deposit which undergoes the most sudden and 
repeated changes which characterize the shore and shoreface 
zones, and we may now turn our attention for a few moments 
to these changes and their causes. 

The Beach. — In the first place, it must be borne in mind that 
the beach is merely a temporary deposit, slowly making its way 
to deeper water. If the various shore processes were perfectly 
uniform in their actions and always nicely adjusted to each other, 
the thickness of the deposit and its surface profile would remain 
essentially the same, while the component particles in the de- 
posit would constantly migrate seaward and be as constantly 
replaced by new material weathered and eroded from the marine 
cliff and bench. But the forces are variable, both in character 
and intensity. Oscillatory waves may be replaced by waves of 
translation at irregular intervals; the undertow varies in volume 
and velocity and is modified by other currents; waves vary in 
size from day to day, and the storm waves of one season are more 
powerful than those of another season. All of these changes, 
and others that might be enumerated, disturb the equilibrium 
which would otherwise exist, and the beach deposit responds 
quickly to these disturbances. At one time wave erosion at 
the base of the cliff supplies material faster than it can be trans- 
ported, and the beach deposit accumulates to a greater depth than 
usual. At another time waves fail to reach the cliff base for a 
long period, and the beach wastes away because the loss it suffers 
from continual attrition and removal under the influence of 
small waves is not made good by new supplies of debris. Again, 
waves of translation drive in much material from the shoreface 
terrace and even from the deeper water beyond, piling it upon 
the normal beach deposit and thereby greatly augmenting its 
thickness. Or storm waves accompanied by a vigorous under- 
tow may sweep the entire beach from the marine bench, leaving 
the bare, solid rock exposed over extensive areas. 

The factors involved in shore processes are so numerous, and 
their variations are so difficult to trace, that it is often im- 



216 DEVELOPMENT OF THE SHORE PROFILE 

possible to ascertain just what disturbance of former conditions 
is responsible for a given change in the beach. ^As Hunt 3 has 
said: " A beach may resist the sea for years, yet in a few hours it 
may be stripped bare to the olid rock. Shells may be covering 
the bottom a mile offshore, undisturbed by onshore gales; a 
storm, with wind and waves apparently much the same as usual, 
may sweep them all onshore. One beach will be invariably 
kept clear of shells which will be found offshore, while another 
beach will have a constant supply, and for no obvious 
reason." 

We may gain some appreciation of the extent of the above- 
mentioned changes in the beach deposit from the published 
reports of competent observers. Reference has already been 
made in an earlier chapter to the shingle and chalk ballast driven 
in upon the beaches between Tyne and Hartlepool, England, 
from points 7 to 10 miles offshore. 4 Along the coast of Algeria 
the waves cast large quantities of sand upon the beach, burying 
the roadway along the shore for considerable distances, a phenom- 
enon well described by Fischer. 5 At one point on the Irish 
coast, according to Kinahan, 6 a beach 200 yards wide was built 
in front of a marine cliff during the spring of 1876, at a point 
where there was deep water the previous winter. The presence 
of a beach deposit along a shore for much of the time is apt to 
give one a false idea of its depth and stability. Thus many 
visitors to the beaches of the Atlantic coast find it difficult to 
realize that a single storm will often strip bare the underlying 
rock or expose buried peat deposits at places where they never 
see anything but an apparently inexhaustible store of beach 
sand. Hunt 7 refers to a case in which the eastern half of the 
shore at Blackpool, near Dartmouth, England, was stripped 
bare of its beach sands, for the only time in twenty-five years so 
far as was known. The bathing beach at Babbicombe was, 
according to this same author, so completely removed by a 
single storm that the place looked Cl as unlike a bathing-cove as 
any place can be." The southern coast of England is well known 
for its extensive beach deposits; yet God wen Austen 8 writes: 
" I have seen, at one time or another, nearly every portion of 
our south coast in the condition of bare rock without sand or 
shingle. . . Bars, sand- and shingle-banks . . . are all subject to 
change of form and to removal, but they speedily collect again." 



MATURE STAGE 217 

During the first few hours of a gale enough material may be re- 
moved from the shoreface to deepen the water there from 5 to 10 
feet, especially where a sea wall helps to concentrate the wave 
energy along a narrow zone. 9 Along the Chesil Bank between 
Abbotsbury and Portland, Coode 10 estimated that a single storm 
removed 3,763,300 tons of shingle from the beach; and during 
another storm_ 4,500,000 tons of the shingle were scoured out, 
three-fourths of which was moved back after the gale ceased. 11 
Pendleton 12 states that the shoreline of the beach along the 
southern coast of Long Island has varied temporarily back and 
forth 200 to 300 feet, due to storms. 

Beach Profile of Equilibrium. — During all the temporary 
changes referred to above, the profile of equilibrium is maintained 
in as great perfection as the rapidly varying conditions will 
permit. Whether developed on the rock bench or on a thick 
overlying beach, the profile is concave upward. The concavity 
continues, with increasingly steep slope, above the normal water 
level, because the swash of the waves sweeps debris up the beach 
and deposits it in such manner as to maintain the necessary equi- 
librium between the onshore and offshore forces. Near the water 
line both the swash and the backwash of the waves have large 
volume and high velocity, and debris is swept back and forth on 
a fairly gentle slope. Farther up the beach the swash suffers loss 
of velocity because of increasing friction and the constant down- 
ward pull of gravity; and loss of volume because much water sinks 
out of sight into the interstices between the beach. pebbles and 
sand. Consequently debris is deposited at the higher level of the 
beach and the backwash is too weak to return it to the sea. But 
the very act of deposition steepens the upper part of the slope, 
thereby increasing the effectiveness of the pull of gravity upon 
the debris, so that a small backwash can the more readily carry 
material back down the slope. Equilibrium is attained when 
the slope is so steep that the backwash aided by gravity can just 
return all the material which the larger swash can drive upward 
against the pull of gravity. In general, it may be said that in 
maturity the beach profile both in the shore and shoreface zones, 
is either nicely adjusted to the conditions imposed by a set of 
waves which have been operating for some time, or is rapidly 
undergoing adjustment to a new set of waves which differ from 
those previously operating. Let us note some of the changes 



218 



DEVELOPMENT OF THE SHORE PROFILE 




in the beach profile which result 
from these adjustments to varying 
conditions. 

Imagine a mature shore profile 
(aaa, Fig. 36) in which a thin 
beach deposit covers the marine 
bench and is continued seaward 
by the shoreface terrace. First 
let us suppose that a series of 
oscillatory waves encountering 
the seaward edge of the terrace 
are partially transformed into 
waves of translation. The waves 
of translation will then drive the 
bottonAIebris landward and bank 
it up against the base of the cliff, 
building the beach deposit for- 
ward and making its front of such 
steepness that gravity plus under- 
tow will just balance the tendency 
of the shoreward component to 
carry material up the slope. But 
the taking of material from the 
bottom deepens the water, and 
deepening water is more and more 
unfavorable to the development 
of waves of translation. The 
waves retain more of their oscilla- 
tory character than formerly; and 
with the more sudden descent 
into deep water in front of the 
new deposit the undertow be- 
comes more effective, finally over- 
coming further efforts toward 
landward transportation. We 
will then have the profile bbb, 
which is the profile of equilibrium 
under the new conditions. 

Now let us imagine that this 
new profile is subjected to the 



MATURE STAGE 219 

action of smaller oscillatory waves, in which the offshore com- 
ponents (backward oscillation + gravity on the steep slope ■+■ 
undertow) are in excess of the shoreward components. Material 
will be eroded from the upper part of the deposit and carried 
seaward. But the undertow associated with these smaller 
waves does not possess a great transporting power. Conse- 
quently much of the seaward moving debris will be quickly 
dropped, thus building up the bottom to a higher level and de- 
creasing the water depth. The effect of this is to restrict the 
undertow within smaller limits and so to increase its velocity until 
it is able to transport all the material eroded by the waves. 
Thus equilibrium between the various factors is once more per- 
fected. Since the load of moving debris is in equilibrium with 
the transporting currents at a higher level than before, a new 
shoreface terrace ccc builds forward over the former bench, and 
possibly over the older terrace. 

Finally, let us imagine that a series of great storm waves, ac- 
companied by a vigorous undertow, attacks the shore under 
consideration. Erosive power is great enough to cut into the 
beach deposit and remove it, and possibly to attack the cliff 
itself; and the seaward currents along the bottom are more than 
strong enough, at the higher level of the profile cc, to transport 
all debris. They therefore erode the bottom, deepening the 
water, and thus decreasing their velocity until they are just able 
to transport the material delivered to them. It may well be 
that this new equilibrium is not reached until the marine bench 
is swept clean and the profile of bench and terrace reduced to 
the line ddd. 

Other changes in the profile of the beach must result from other 
variations in the on- and offshore forces. An offshore wind may 
cause a landward bottom current, as we have already seen, and 
this, aided by wave agitation, builds the beach forward until the 
front slope is so steep and the water so deep that equilibrium is 
restored. An onshore wind may develop such a vigorous under- 
tow that the bench will be stripped of much of its deposits be- 
fore equilibrium is again reached. This would explain Coode's 13 
observation that after offshore winds the slope of a shingle beach 
is 1 in 3| or 4; whereas after heavy onshore winds the slope is 
only 1 in 9 or 9J. If the supply of waste from the cliff is stopped 
for any reason, the beach will be removed and the bench lowered 



220 DEVELOPMENT OF THE SHORE PROFILE 

to a new profile. On the other hand, if a change in the character 
of cliff material should result in a more rapid supply of debris, 
the seaward currents will be too weak to transport all the debris 
until deposition has shallowed the water and thereby increased 
the current velocity; or, as Fenneman 14 has expressed it : " If the 
supply of material be suddenly increased, a smaller shelf will 
grow from shore on the surface of the older, for the reason that 
the new load, being greater, is in equilibrium with the currents at 
a higher level than before." In all of these and other similar 
changes, the profile of equilibrium is either maintained or quickly 
restored. 

From what has been said in the preceding paragraphs, it is 
evident that man has the power to retard cliff erosion if he can 
deposit a sufficient amount of debris upon the shore to overload 
the waves and cause them to establish a profile of equilibrium 
which does not touch the bare rock of bench or cliff. On the 
other hand, man may accelerate cliff erosion by removing sand or 
shingle from the beach, thereby causing the waves to expend 
their excess energy in retrograding the shoreline until a new 
profile of equilibrium is established. Legal authorities have taken 
cognizance of this latter possibility in a number of cases. Thus 
the British Board of Trade has repeatedly prohibited the removal 
of beach material from shores where it was clear that such re- 
moval would be injurious to the coast. In an action brought by 
the Attorney General against a certain lord who asserted his 
right to remove shingle from his own shores, it was held that it 
was the duty of the Crown to protect the realms from inroads of 
the sea by maintaining the beaches in their natural condition; 
and an injunction was granted restraining any further removal. 15 
When the removal of shingle from the beach at Spurn Point, 
England, for road mending and concrete, was stopped, the 
erosion of the cliffs diminished one-half. 16 On the Prussian 
shores the taking of stones from the beach is " polizeilich ver- 
boten." 

I have dwelt at some length upon the local and temporary 
variations in the profile of equilibrium, in order to make clear 
their essential unimportance so far as the whole cycle of shore 
profile development is concerned. This is the more necessary 
because the true significance of these changes has not been as 
widely understood as one could wish were the case. Long ar- 



MATURE STAGE 221 

tides have been written, extended discussions have been carried 
on, and numerous erroneous laws of shoreline activity have been 
laid down, all based on observations of minor fluctuations in the 
shore profile of equilibrium. This has been unfortunate for the 
development of that part of the science of physiography relating 
to shorelines, for two reasons: It has concentrated attention on 
the less important details of shore activities, and caused a neg- 
lect of the broader and more fundamental aspects of coast 
erosion; and it has led to endless controversy regarding the 
conditions of wave erosion and deposition, and the relative im- 
portance of waves, winds, and tides in controlling the direction 
of debris migration along the coast. 

The problem of longshore debris migration will be taken up 
in a later paragraph. Emphasis may here be laid upon the fact 
that the shore profile of equilibrium represents a condition of 
balance, not between two forces but between many forces. 
Whether a beach will be eroded or will have material added to 
it does not depend upon the number of waves which arrive per 
minute; nor upon whether the waves are groundswells or local 
wind waves; nor upon whether the waves strike the beach 
obliquely or at right angles; nor upon whether the wind blows 
with the waves or against them; nor upon whether the waves 
run with the tide or against it; nor upon whether the waves 
are of the oscillatory or translatory variety. Absolute rules 
regarding the behavior of beaches under each of the above con- 
ditions have been published, some of which have been quoted 
on previous pages. Yet all these rules are necessarily fallacious 
because they take no account of the fundamental fact that 
beach erosion or deposition must ultimately depend upon whether 
or not the profile is in equilibrium with the resultant of all the 
forces operating upon it. In a complex of forces, it is not per- 
missible to pick out some one force and attempt to build theories 
upon its sole activity; for it may well happen that its effect 
may be overcome by the superior power of other forces associ- 
ated with it. We can thus readily understand the fact that every 
" rule of thumb," relating to wave action on beaches, yet pro- 
posed has been vigorously assailed by men whose observations 
directly contradicted it. I shall hope to show in the pages 
which follow that the matters thus elaborately debated are of 
relatively small consequence, in view of the fact that the ultimate 



222 DEVELOPMENT OF THE SHORE PROFILE 

tendency of all wave action is to erode the lands. The tempo- 
rary variations in beach and bench profiles are insignificant 
incidents in the relentless advance of the waves into the heart 
of the continents. 

Effect of Longshore Currents. — Thus far attention has been 
directed to the very temporary changes in the shore profile result- 
ing from variations in the activity of on- and offshore forces. Let 
us now consider the effect of longshore current action upon the 
shore profile of maturity. In the first place, if the longshore 
action be in the nature of beach drifting it is evident that any- 
thing which locally stops that movement must force a readjust- 
ment of profiles on both sides of the obstruction. For there will 
be an undue accumulation of material on the near side of the 
obstruction, causing a prograding of the shore until the profile is 
steep enough to allow the offshore forces to dispose of the excess 
material. On the far side of the obstruction the shoreline will 
be retrograded, because the failure of the longshore supply of 
debris will leave the shore forces with an excess of energy which 
will be expended in erosion. It is for this reason that the erec- 
tion of a pier or groin, extending out from a gravelly or sandy 
beach, is usually followed by an advance of the beach on one 
side and a cutting away of the beach on the other side of the 
structure. 

If the longshore movement be in the nature of a more exten- 
sive current located some distance offshore, the results may be 
far more impressive. Imagine a shore in which the profile of 
equilibrium is established, and is being gradually pushed land- 
ward under wave attack, accompanied, of course, by the minor 
fluctuations in beach profiles which have been discussed above. 
Now let us suppose that a broad current of any type flows paral- 
lel with the shore, bringing with it much debris, a part of which 
is deposited in the offshore zone. Continued deposition shal- 
lows the water, thus favoring the development of waves of trans- 
lation. As we have already seen, waves of this type tend to 
remove the deposited material from the bottom and drive it 
landward, adding it to the front of the beach. Normally, the 
effect of this action is to leave deeper water offshore, which is 
in turn unfavorable for the development of waves of translation. 
But in the case before us the longshore current continually 
shallows the bottom by deposition; hence waves of translation 



MATURE STAGE 223 

may continually form, and constantly add material to the front 
of the beach. Just so long as the current aggrades (builds up) 
the seabottom offshore, the waves will prograde< (build forward) 
the shore. Following Davis we may call any shore which is 
experiencing such a long-continued advance into the sea, a 
prograding shore, and distinguish it from the more usual retreat- 
ing or retrograding shore. 

The prograding of a shoreline may take place rapidly or 
slowly, and may continue for a few years, a few centuries, or 
many thousands of years. According to Marindin 17 the beach 
at Siasconsett, Nantucket Island, has advanced 255 meters be- 
tween the years 1846 and 1890. A beach in front of a marine 
cliff at Nantasket, Massachusetts, has grown seaward 400 meters 
or more during a period estimated at one to three thousand 
years. 18 The shore of the Darss, in northern Germany, has been 
prograded 7000 or 8000 meters since about the year 2000 B. C. 00 
and a somewhat greater length of time was probably required 
for the advance of Cape Canaveral a similar distance into the sea.^ 
It should be borne in mind, however, that these long-continued 
additions to the land, while far more important and significant 
than the minor fluctuations previously discussed, are themselves 
only temporary effects of longer duration, and that in a compara- 
tively short fraction of the whole shoreline cycle they must be 
cut away. This point will be further considered on later pages. 

Longshore currents which have a fairly high velocity but which 
bring little or no sediment to deposit, may help to keep the 
marine bench swept clean of debris, thus materially aiding the 
retrograding of the shoreline. It is probable that some of the 
localities where a broad marine bench is usually well exposed, 
as for example off some parts of the coast of Brittany, owe the 
exposure of the bench to the effective assistance which wind, 
tidal, or other currents lend to the normal on- and offshore 
processes. 

There remain for consideration one or two minor features, of 
the shore profile of maturity. The landward portion of the 
profile is apt to be complicated by a series of " storm beaches " 
or " storm terraces." representing the effects of waves of vary- 
ing dimensions at different heights of the tide. Such backshore 
terraces often have a faint landward slope on their upper sur- 
faces. This is due to the fact that over wash from the highest 



224 



DEVELOPMENT OF THE SHORE PROFILE 



waves flows across the terrace, depositing a larger 
proportion of its load near the seaward edge, 
where its velocity is first checked and its volume 
is rapidly decreasing from loss of water sinking 
into the porous beach deposit. The front of each 
terrace may represent the upper part of a former 
beach profile of equilibrium; or it may be an 
erosion scarp if waves at lower levels have cut 
into the former profile, instead of merely deposit- 
ing debris in front of and upon it. Beach 
cusps 20 may give the front of any backshore 
terrace a serrate plan. 

The shoreface terrace has an upwardly con- 
vex profile at its seaward margin, as we have 
already noted; but the foot of the terrace may 
have a concave profile due to deposition from 
suspension. 21 

Old Stage. — In Figure 37 the profile aW 
represents a partially submerged land mass with 
a mature shore profile at a 2 where we see the 
cliff, bench, and terrace which are shown on 
a larger scale in Figure 35, cP-cPd 3 . On the scale 
of Figure 37 it is not practicable to represent 
the beach deposit on the bench, but its presence 
may be inferred. The profile b l b 2 b s is the profile 
of early old age, and c l c 2 & the profile of advanced 
old age of this same shore. It will be noticed 
that in early old age the cliff (b 2 ) has a very 
faint slope, scarcely meriting the name " cliff," 
except in a technical sense; for wave erosion 
must proceed slowly when the waves have to 
traverse the vast expanse of shallow water over 
the wide abrasion platform which they them- 
selves have cut, and when all debris must slowly 
be moved from the cliff to the edge of the terrace 
at b 1 before it reaches a final resting place. The 
marine bench is still to be found in front of 
the cliff; but it merges imperceptibly into the 
similar but much larger and more faintly in- 
clined erosion surface which we have just referred 



OLD STAGE 225 

to as the abrasion platform. The continental terrace (6 1 ) is 
developed on a large scale; and the abrasion platform, normally 
covered with a thin marine veneer in excessively slow transit, is 
now so broad that, in combination with the continental terrace, 
it gives a very extensive continental shelf. One would scarcely 
expect all eroded debris to be transported to such a distance as 
to leave a continental shelf consisting wholly of an abrasion plat- 
form, although this appears to be Vogt's idea of the " konti- 
nentale plattform" off the northern coast of Norway. 22 Erosion 
and weathering have reduced the former upland (a 3 ) to a series 
of broad valleys separated by subdued divides of moderate 
elevation (¥). 

In advanced old age the cliff (c 3 ) has been pushed much farther 
inland, and is so low and flat that it is almost imperceptible. 
The remaining land area has been worn down to a peneplane of 
faint relief. Abrasion platform (c 2 ) and continental terrace (c 1 ) 
are much broader than before. Waste is supplied so slowly 
from the land that the abrasion platform is gradually denuded 
of its veneer, and the vast extent of continental shelf may con- 
sist largely of bare rock on the landward side and sedimentary 
deposits on the deep-water side. 

Wave Base. — The final stage of marine erosion will have been 
reached when the entire land mass is reduced to an ultimate abra- 
sion platform surrounded on all sides by a continental terrace, the 
level of the platform being as far below the surface of the sea 
as wave erosion is effective. In other words, the cycle of 
marine denudation is completed when all the land is reduced to 
the baselevel of wave-erosion, just as the cycle of fluvial denu- 
dation is completed when all the land is reduced to the baselevel 
of stream erosion. The valuable term " wave base " was in- 
troduced by Gulliver 23 to denote the imaginary plane down to 
which wave action tends continually to reduce the lands; and 
since, as we have seen, the lower limit of effective wave work is 
probably reached at a depth of about 600 feet, we may tenta- 
tively consider wave base as an imaginary plane about 600 feet 
below the surface of the sea. A cycle of wave erosion ends, 
therefore, when all the land is reduced to a plane surface about 
600 feet below sealevel. 

A common error is to confuse wave base with profile of equi- 
librium. The gently sloping subaqueous terrace bordering lake 



226 DEVELOPMENT OF THE SHORE PROFILE 

shores or the shores of a sea, and the submarine platforms of 
islands truncated by ocean waves, are frequently explained as 
the products of wave erosion down to wave base, when in fact 
they merely represent surfaces of equilibrium which are very 
slowly being reduced toward a wave base far below. The Platte 
River has established its profile of equilibrium at a level which 
is in places some thousands of feet above the sealevel, and to 
ordinary observation does not now appear to be cutting its valley 
any deeper. Yet no one would make the mistake of saying that 
the valley floor of this stream had been reduced to baselevel. 
It is no less erroneous to say that a subaqueous terrace on which 
the marine forces are now in equilibrium and which shows no 
evident indications of being cut deeper, has been reduced to 
wave base. The error is compounded when the false assumption 
that the terrace represents wave base is made the ground for the 
conclusion that wave action is not effective below a compara- 
tively shallow depth. Equilibrium may be established at a shal- 
low depth; from that level downward wave erosion proceeds 
more and more slowly, but none the less surely. 

It might seem on first thought that no limit could be set to the 
depth of wave action, because theoretically waves of translation 
affect the water on the bottom as much as they do the surface 
layers, no matter what the water depth may be. We have 
already seen, however, that waves of translation are more apt to 
be formed in the shallow waters surrounding the lands, since con- 
ditions favorable to their development seldom exist in the deep 
sea. Another point of much importance in this connection is 
that waves of translation, when propagated into deep water, tend 
to change into oscillatory waves, as has been shown by Rankine. 24 
It would seem to follow from this that the ordinary waves of 
translation found near the shores cannot be efficient agents in 
lowering the level of wave base, because they cease to exist as 
such when the water attains any considerable depth. 

Gulliver 25 states that the abrasion platform " will not lie as 
far below the surface of the sea [in late old age of shore develop- 
ment] as it did in its maturity." Such a statement suggests that 
Gulliver confused the plane of denudation or abrasion platform 
with the submarine plain of deposition formed by the marine 
veneer laid down upon the platform. Even so, it is difficult to 
see how the marine veneer could become thicker in the late old 



OLD STAGE 



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228 DEVELOPMENT OF THE SHORE PROFILE 

age of shore development, thereby shallowing the sea. There is 
a slight tendency in this direction at" an earlier stage; but in late 
old age the supply of debris from the land is decreased and the 
abrasion platform must be denuded of its veneer, as already 
shown. 

Validity of the Theory of a Marine Cycle. — Thus far I have 
for the most part assumed the theoretical possibility of extensive 
marine erosion to wave base, and have only incidentally re- 
ferred to contrary opinions. It is only proper, however, that we 
fairly consider any objections to the theory of marine planation 
and determine whether they invalidate any of the conclusions 
reached above. 

Wave-cut Benches. — One finds no reason to doubt that wave 
erosion has produced more or less plane surfaces of moderate 
breadth around the margins of certain lands. The very striking 
pre-glacial shore terrace (Plate XXVI) bordering the western 
isles of Scotland is described by Wright 26 as an uplifted platform 
of marine erosion having a breadth of about half a mile in places, 
part of the breadth having been lost through later wave erosion 
at present sealevel. Lawson 27 has described uplifted wave-cut 
rock platforms on the coast of California having a maximum 
width of more than a mile. Comparatively rapid emergence of 
the land prevented long-continued wave attack at one horizon, 
with the result that the platforms constitute an extensive series 
of terraces (Fig. 38), the highest pf which is over 1500 feet above 
sealevel. There can be no doubt that had all this erosive work 
been performed at one horizon the resulting platform would 
have been much broader than any one of the existing wave-cut 
surfaces. Comparatively weak waves on Lake Michigan attack- 
ing shores of glacial drift have formed a terrace whose outer 
margin is approximately 60 feet below the lake surface, and 
which varies in breadth from 2 to 6 miles, with a maximum at one 
locality of 12 miles. Andrews 28 assumed that the entire breadth 
of the terrace was due to wave erosion; and proceeding on 'the 
further assumption that the rate of wave erosion is the same 
during all stages of terrace cutting, he used the breadth of the ter- 
race and the present known rate of cliff retreat to establish a 
measurement of post-glacial time. Both his assumptions must 
be considered erroneous; but it seems probable that from one to 
several miles of the terrace breadth is wave-cut, even though a 




(229) 



230 DEVELOPMENT OF THE SHORE PROFILE 

large part of it represents the effect of wave deposition. In a 
paper entitled " Fenomeni di abrasione sulle coste dei paesi dell' 
Atlante " 29 Fischer describes a submarine terrace bordering parts 
of the north coast of Africa having an outer margin approxi- 
mately 100 to 200 meters below the surface of the Mediter- 
ranean, and a maximum breadth of at least 12 miles. The en- 
tire breadth of this terrace is regarded by Fischer as a marine 
abrasion platform; but it seems probable that the outer part 
of it is of constructional origin. Good photographic illustrations 
of its exposed landward margin, where it is an undoubted plat- 
form of marine abrasion, accompany the same author's report 
on " Ktistenstudien und Reiseeindrucke aus Algerien," 30 while 
a short description of the terrace occurs in an earlier paper on 
" Ktistenstudien aus Nordafrika." 31 It is well known that cer- 
tain volcanoes formed in the ocean have been reduced by wave 
erosion to submarine platforms within the space of a few years, 32 
and there are excellent reasons for believing that many of the 
more or less circular submarine platforms in the Pacific Ocean 
described by Wharton 33 and other writers, and more recently 
discussed by Daly 34 in connection with the glacial-control theory 
of coral reefs, represent volcanoes whose summits have been 
truncated by marine abrasion. Not a few of these platforms 
measure from 20 to 30 miles or more in diameter, but what 
portion of the whole represents marginal deposits of debris eroded 
from the center is unknown. 

The great wave-cut platform (" strandnaden " of the Nor- 
wegians) fringing the west coast of Norway, best known through 
the studies of Reusch, 35 Richter, 36 Vogt 37 and Nansen, 38 has an 
average breadth of nearly 30 miles, and a maximum breadth of 
nearly 40 miles according to Vogt and Nansen, if we include the 
portion still submerged. Notwithstanding the doubt implied 
by Reusch, and clearly expressed by Hansen 39 and Nussbaum 40 
regarding the essential marine origin of this topographic feature 
it is generally considered, and probably correctly so, one of the 
best examples of marine abrasion on a large scale yet discovered 
along our present coasts. Nansen 41 describes similar platforms 
of marine abrasion fringing the coasts of Siberia, Greenland 
and other land areas, none of which are so broad as the Norwegian 
case, although a breadth of nearly 20 miles is not unknown. 
The east coast of India, as described by Cushing, 42 consists 



VALIDITY OF THE THEORY OF A MARINE CYCLE 231 

in part of a remarkably smooth, uplifted plane of marine 
denudation, above which rise numerous unconsumed rem- 
nants of quartzite, the bases of these former islands or stacks 
not infrequently being marked by sea-caves (Plates XXIX- 
XXXI). In places this wave-cut plane attains a breadth of 
about 50 miles. 43 

It seems highly probable that considerable portions of the 
continental shelves bordering certain shores represent plat- 
forms of marine abrasion. Nansen 44 is of the opinion that a 
great part of the continental shelf west of Norway is of this 
origin, and believes that between latitude 65° 10' N. and 66° N. 
solid rock is present clear to the edge of the shelf. Figure 39 
represents two of Nansen's sections for this region, in which the 
results of soundings are indicated. Notwithstanding the diffi- 
culty of determining the presence of solid rock by the sounding 
method, Nansen believes that the rocky ridge shown near the 
outer margin of the shelf is correctly indicated. If he is right 
we have here a plane of marine abrasion, including the rocky 
" coast platform " described above, exceeding 170 miles in 
maximum breadth. 

It is true that Nansen doubts the power of waves to carve a 
broad and gently sloping platform on a simple coast; and he 
therefore assumes that even in the case of the narrower " coast 
platform " or " strandfladen " the coast was first deeply in- 
dented by fjords, and the platform later cut during glacial and 
interglacial periods by wave attack from both the ocean and 
the fjord waters, aided by subaerial denudation. 45 We must 
doubt the validity of the theoretical grounds on which he thus 
limits the power of waves in the open ocean; and must like- 
wise doubt whether small waves in sheltered fjords, formed as 
they are on the surface of deep water and therefore unarmed 
with debris, and subject to reflection from nearly vertical rock 
walls without opportunity for erosion, could materially aid in 
the process of reducing a land mass to a submarine platform. 
Neither do his arguments in favor of the glacial age of the coast 
platform appear convincing 46 . But the facts presented by this 
author leave no room to doubt the existence along the west 
coast of Norway of a wave-carved platform which is certainly 
50 to 75 miles broad, and possibly as much as 170 miles broad 
in some of its parts. 




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VALIDITY OF THE THEORY OF A MARINE CYCLE 233 




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234 DEVELOPMENT OF THE SHORE PROFILE 

Theory of Marine Abrasion. — It is evident from the brief 
survey given above that planes of marine abrasion a great many 
miles in breadth are well-attested features of the earth's surface. 
But it is difficult or impossible to tell whether or not these planes 
were formed during a still-stand of the land or during a progres- 
sive submergence. There is a widespread idea that waves can cut 
into a still-standing land mass only to a very moderate extent 
before they will exhaust themselves on the shallow bench which 
they have carved. According to this interpretation, a marine 
cliff will be pushed inland by the waves for a short distance, and 
will then remain unchanged in position unless subsidence of the 
land mass deepens the water on the marine bench and thus per- 
mits waves once more to erode the base of the cliff. Marine 
planation would only be possible, therefore, on a subsiding land 
area. This view is expressed by von Richthofen 47 in his great 
work on China, where he states that slow depression alone can 
produce regional abrasion, since without progressive sinking the 
waves soon become exhausted on a narrow platform of their 
own carving. The same idea is expressed in his " Ftihrer fur 
Forschungsreisende " 48 . De Martonne, in his " Traite de Geo- 
graphic Physique " 49 ; de Lapparent in his " Traite de Geologie " 50 
and his " Lecons de Geographie Physique" 51 ; Kayser in his 
" Lehrbuch der Geologie " 52 ; and Scott in his "Introduction to 
Geology " 53 are among the text-book writers who have adopted 
von Richthofen' s theory that waves cannot cut far into the land 
unless wave erosion is aided by coastal subsidence. Many others 
have taken the same position, and some have even gone so far as 
to cite wave erosion as an indication of land sinking. For exam- 
ple, Hahn 54 says we must suspect a sinking of every region which 
suffers loss through the washing away of its margin, and Haage 55 
gives wave erosion as one of the distinguishing characteristics of 
a sinking coast. 

On the other hand, there are a few who have maintained that 
waves will continue to cut into any land mass so long as it pro- 
jects above sealevel, whether or not it is undergoing depression. 
Ramsay, the first to recognize the power of the waves to produce 
a plane of abrasion, clearly expresses his belief that while sub- 
sidence of a land mass will aid the process of marine erosion, it 
is not essential; since, " taking unlimited time into account," 
any land area must eventually be worn away by the waves 56 . 



VALIDITY OF THE THEORY OF A MARINE CYCLE 235 

Green seems equally convinced of the ability of wave erosion to 
produce an extensive plane of denudation without subsidence, as 
he explains the origin of such planes without mentioning changes 
of level 57 . Both of these authors failed to appreciate the con- 
siderable depths to which wave action extends, Ramsay assuming 
that " the line of denudation " is " a level corresponding to the 
average height of the sea," while according to Green marine 
denudation must reduce a country to " an even surface coin- 
ciding approximately with the level of the lowest tides." Jukes- 
Browne 58 was almost as conservative in his estimate of the 
depth of marine erosion. Davis 59 , Gulliver 60 , and Fenneman 61 
are among those who recognize not only the possibility of in- 
definite wave erosion on a stable land mass, but the additional 
fact that the baselevel of wave erosion is located at an appreci- 
able depth below the water surface. 

In the opinion of the writer any careful analysis of the process 
of marine erosion must lead to the conclusion that marine pla- 
nation is possible without coastal subsidence. We have already 
seen that where the resultant of wave action is landward, material 
is driven toward the shore until the steepening of the shore pro- 
file produces a condition of equilibrium in which material driven 
up the slope by the landward-acting forces returns again under 
the combined influence of gravity, undertow, and other seaward- 
acting forces. During the entire period of equilibrium, sand, 
pebbles, and shingle are driven back and forth, up and down the 
beach slope, continually grinding themselves finer and finer. 
In this gigantic mill which borders the lands, rock fragments 
are continually reduced to a state of such exceedingly fine com- 
minution that they are readily removed from the shore'and shore- 
face zones as suspended particles in the water. During and 
after heavy wave action the water is turbid with matter in 
suspension to a considerable distance from the land. Part of 
this suspended matter is removed far from shore by the many 
currents which are involved in oceanic circulation, and finds a 
permanent resting place beneath the quiet waters of abysmal 
depths. 

If there is an absolute loss of land where the resultant of wave 
action is landward, and the shore profile is built forward until 
equilibrium is established, how much greater must be that loss 
when the seaward components of wave agitation prevail and 



236 



DEVELOPMENT OF THE SHORE PROFILE 




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VALIDITY OF THE THEORY OF A MARINE CYCLE 237 

coarser debris on the bottom, as well as material in suspension, 
is transported seaward to be deposited over the edge of the 
continental shelf. Account must also be taken of the fact that 
agitation of the marine veneer is continually grinding its par- 
ticles smaller and grinding material from the solid surface of 
the abrasion platform, thus producing fine sediment which cur- 
rents may readily carry to deeper water during and after vigorous 
wave action. The never-ending shifting of the beach deposit 
back and forth over the shore and shoreface, already fully de- 
scribed, is accompanied by a ceaseless loss of the finest attrition 
products. Whether the shore profile is in equilibrium or not, 
whether waves are depositing beach material or sapping cliff 
bases, whether the marine veneer is increasing or decreasing in 
volume, there is a constant loss of very fine matter which is 
borne far away to deep water by current action. This means 
an eventual loss of equilibrium which must ultimately be re- 
stored by the erosion of more material from the lands. Where- 
ever there is wave erosion there is an absolute loss of material 
from the lands attacked. The laws of wave action afford no 
basis for Mitchell's conclusion that the sea restores to the con- 
tinent " all the material washed from its bluffs and headlands " 62 . 
On the contrary, we must conclude that the sea never restores 
anything to the continent, except temporarily. The surface 
extent of lands temporarily built by marine agencies may be 
great, but their total volume above sealevel is small as compared 
with the volume removed by marine erosion. There was much 
of truth in the statement made nearly a century ago by Robert 
Stevenson, to the effect that " these apparent acquisitions are 
no more to be compared with the waste alluded to, than the 
drop is to the water of the bucket 63 ". In the end the tempo- 
rarily restored materials must themselves suffer removal by the 
combined action of waves and currents, which, however slowly, 
yet unceasingly destroy any land mass exposed to their attack. 
Under the most unfavorable conditions the loss from the lands 
will be small, but real. Where conditions favor vigorous wave 
erosion, rapid disintegration of the rock fragments, extensive 
solution of the rock-forming minerals, efficient transportation 
of the mechanical debris offshore, and high current velocities 
continued to deep water, the wasting of the land 'may be ex- 
ceedingly rapid. 



238 DEVELOPMENT OF THE SHORE PROFILE 

It is not possible that waves should exhaust themselves upon 
a platform of their own carving, and thus fail after a time to con- 
tinue cliff erosion; for the loss of wave energy means that that 
energy has been expended upon the platform in question, and 
energy so expended can have but one result: abrasion and con- 
sequent lowering of the platform. This partially removes the 
cause of wave exhaustion, so that later waves reach the cliff 
base with enough energy remaining to effect some slight erosion. 
Any surface shallow enough to retard wave attack must suffer 
denudation until the attack is resumed. The vertical limit of 
marine denudation is a surface so low that wave action is no 
longer retarded by it. The corollary of this is that there is no 
horizontal limit of marine erosion. 

In this connection it should be pointed out that fairly rapid 
wave cutting may occur at the base of a cliff which has been 
pushed far into the land. This arises from the fact that the 
shore profile must change extensively at times because of large 
variations in the forces attacking the shore. Imagine, for ex- 
ample, that on a shore which had been in nearly perfect equi- 
librium under gradually weakening wave attack for so long a 
time that the beach deposit had wasted away to a very small 
volume, a series of unusual storms should drive in vigorous 
oscillatory waves and develop a strong undertow. It is quite 
conceivable that the cliff, which had for years scarcely been 
touched by the waves, might be steepened and driven inland 
with comparative rapidity. In this case the average rate of cliff 
retreat would be exceedingly small; but the absolute rate for a 
limited time might be high. Variations in the direction and 
strength of longshore currents might also be accompanied by 
increased rate of cliff recession, in any place where such vari- 
ations materially affected the condition of the shore profile. 
Even fairly rapid cliff retreat on a late mature or old shore 
profile is not, therefore, necessarily proof that coastal sub- 
sidence has admitted larger waves by deepening the water 
offshore. 

Effect of Deposition. — One might suppose that the deposition 
of organic or chemical sediments from the water above the abra- 
sion platform would protect the platform from erosion and by 
preventing its further deepening eventually stop further cliff ero- 
sion. But a little consideration will show that such deposition 



VALIDITY OF THE THEORY OF A MARINE CYCLE 239 




240 DEVELOPMENT OF THE SHORE PROFILE 

can only bring about an elevation of the general level at which 
marine planation will occur. In the early part of the shore cycle, 
when deposition is small and erosion vigorous, the platform will 
be rapidly lowered. Later, when the increased depth of water 
over the platform permits more extensive deposition of organic 
or chemical sediment from the increased volume of superjacent 
water, and at the same time results in decreased intensity of 
wave erosion on the platform, the contending forces will be 
more nearly balanced. Equilibrium will be established and the 
effective wave base reached, when wave agitation and current 
action combined can just effect the removal of the deposits 
which tend to accumulate on the platform. Were it not for the 
burden of removing these deposits, the waves would reduce the 
platform still lower. 

It is sometimes stated that before waves can erode cliffs far 
into the lands, rivers will bring out vast quantities of sediment 
which will in turn be widely distributed along the shores by 
currents. Deposition of the sediment, it is argued, will shallow 
the water, proteet the shores and sea-bottom, and effectively pre- 
vent further cliff retreat. This argument assumes that the 
quantity of debris brought out by rivers and distributed along 
the margins of the lands is equal to or greater than the quantity 
of debris which the marine forces are competent to remove, 
and that therefore the entire energy of those forces is consumed 
in handling river-brought material. While it seems to the 
writer that as a general proposition this assumption is untenable, 
we may temporarily grant its reasonableness for sake of argument, 
providing it refers to a youthfully or maturely dissected land 
mass. As the land wears lower and the streams become more 
sluggish, the latter will bring to the sea a decreasing amount of 
sediment, an increasing proportion of which will be carried in 
suspension and so will be borne out to deep water without 
pausing in the vicinity of the shores. The forces of marine 
erosion and transportation will eventual^ remove the deposits 
which impeded wave attack during an earlier part of the fluvial 
cycle of land dissection, and once more the relentless encroach- 
ment of the sea will be manifest. Under the assumption least 
favorable to wave erosion, therefore, the progress of marine 
planation cannot be stopped by river-brought sediment. It 
can only be delayed. Deltas may be built seaward against the 



VALIDITY OF THE THEORY OF A MARINE CYCLE 241 



Plate XXX. 




Photo hg S. W. Gushing. 
Base of monadnock in Plate XXIX, showing effects of marine erosion. 



242 DEVELOPMENT OF THE SHORE PROFILE 

weves for a time, and help to keep parts of the shoreline young; 
late-mature coasts*are delta-free. 

The direct effects of river sediments in preventing cliff erosion 
have been exaggerated, as intimated in the foregoing paragraph. 
Near the mouth of many rivers it is perfectly apparent that the 
river deposits are directly shielding the cliffs from wave attack. 
But active cliffing is going on along many other coasts in spite 
of the fact that numerous streams enter the sea through valleys 
opening in the face of the cliffs; while long stretches of coast 
have enormous accumulations of beach deposits demonstrably not 
of fluvial origin. When we come to consider the deposits in the 
offshore zone, however, it is probable that greater importance 
must attach to stream-brought sediments, and that indirectly 
they may play an important role in certain stages of the marine 
cycle. Let us analyze, if possible, the relation of the marine cycle 
to the fluvial cycle of land dissection. 

Correlation of the Marine and Fluvial Cycles. — Imagine a 
newly uplifted land mass of great areal extent and irregular sur- 
face, attacked at once by wave and stream erosion. During the 
youthful stage of stream development sediment is being eroded 
from some parts of the stream profile only to be deposited else- 
where as filling for lake basins, as alluvial fans, flood plains, and 
other temporary accumulations. Only a small part of the sedi- 
ment reaches the sea. During this period the shore profile is 
in the young and perhaps early mature stages of its development, 
the abrasion platform is being rapidly developed, and the cliffs 
are being pushed steadily inland. Since river-brought sediment 
is small in amount at this time, the development of the shore 
profile is not greatly affected by it. 

When the drainage system on the land is thoroughly inte- 
grated, all its parts nicely adjusted, and the stream profiles of 
equilibrium perfected, sediment from all parts of the land sur- 
face is ceaselessly swept seaward. At the river mouths the 
coarser sediment may be deposited in a delta, or driven along the 
shores in either direction. The finer material will be trans- 
ported to a greater or less distance by some of the many types of 
marine currents, and much of it deposited in the offshore zone. 
By this time the marine cliff has' been pushed well into the land, 
the abrasion platform has attained a considerable width, and a 
thin layer of marine veneer is journeying slowly down the sub- 



CORRELATION OF THE MARINE AND FLUVIAL CYCLES 243 

marine slope toward the edge of the continental terrace. In- 
creasing volumes of river-brought sediment are now deposited 
upon the shelf, adding to the thickness of the marine veneer and 
continental terrace, and thereby shallowing the water of the off- 
shore zone. Aggrading will continue until a level is reached where 
the increased wave and current agitation is sufficient to remove 
the amount of debris which is deposited. The new profile 
of equilibrium will hardly rise to the surface of the sea, except 
under exceptional conditions in limited areas, as where deltas 
are temporarily formed. Coasts bordering shallow inland seas, 
or otherwise protected from the full attack of destructive marine 
forces, may, like the coasts of Holland and Belgium, be built far 
forward by delta accumulations before the inevitable period of 
their removal begins. Especially will this be the case if lands 
raised to mountainous heights shed debris into the sea through 
many rivers with exceptional rapidity. Both modern and 
ancient examples of coasts where conditions favored extensive 
delta growth are cited by Barrell 64 , who fully recognized the tem- 
porary nature of the delta protection of coasts. Around most 
of the land margin, where delta protection is lacking, smaller 
waves will continue to traverse the waters shallowed by the 
deposition of river-brought debris, and will continue to erode 
the cliff, but more feebly than before. Cliff retreat, already 
slow because of the increasing breadth of the offshore zone, will 
be still further retarded by virtue of the decreased depth of 
water in that zone. Maturity of land drainage, therefore, 
means retarded shoreline development. 

As the rivers of the land approach old age, they become more 
sluggish. Meandering in circuitous courses on a very low 
gradient, they can transport but a limited volume of the finest 
sediment. Decreased land relief is accompanied by decreased 
rainfall and increased loss of water by evaporation; and this 
means diminished stream volume. A smaller quantity of finer 
debris is weathered from the very gentle slopes of the old valley 
sides, to be carried to the sea by shrunken and enfeebled rivers. 
More material is removed in solution; less and finer material is 
removed in mechanical suspension. Upon reaching the sea much 
or all of this very fine material may be transported far from the 
land by marine currents before deposition is possible. Waves 
and currents in the offshore zone are no longer over-burdened 



244 DEVELOPMENT OF THE SHORE PROFILE 

with river deposits, and expend their excess energy in removing 
the material previously deposited. The depth of the water is 
increased until the abrasion platform is again exposed to the 
slow wear of the migrating marine veneer. Larger waves gain 
access to the land, and cliff erosion is relatively more effective 
than before. But increased breadth of the abrasion platform 
and continental terrace compels material eroded from the cliffs 
to make a longer journey to deep water; and the longer time 
necessary to dispose of cliff debris necessarily tends to retard 
cliff recession. On the other hand, the reduction in land relief 
accomplished by the subaerial forces gives a lower marine cliff 
from which a smaller amount of debris is offered to the waves 
and currents for removal. Current action along the smoothed- 
out contours of mature and old shores may be much more effec- 
tive than on the more irregular shores of youth; and the conse- 
quent more effective removal of debris from the shores may com- 
pensate, in part at least, for the greater distance to which it must 
be removed. All things considered, it seems to the writer that 
the retrograding of the shoreline must proceed more rapidly 
during the old age of land dissection than during its maturity. 
Especially must this be true where the reduction of extensive 
land areas by subaerial denudation causes a progressive rise of 
sealevel due to the infilling of sediments in the ocean basins. 
The significance of these relationships in the cycle of marine 
sedimentation has already been ably discussed by Barrell 65 in 
his essay on the " Relative Geological Importance of Continental, 
Littoral, and Marine Sedimentation." 

The foregoing considerations lead to the interesting conclusion 
that, other things being equal, marine erosion should proceed 
most effectively about the low-lying desert areas of tropical 
regions, especially on the windward sides of such areas. For 
the absence of rivers would permit the development of the shore 
cycle, unretarded by any land sediments except the very fine 
material borne seaward by the winds. On the windward side 
even the seolian deposits would be lacking, while the onshore 
winds would continually drive vigorous waves against the cliffs, 
and by elevating the water surface would tend to produce a strong 
undertow which would assist in removing the products of wave 
erosion to deep water. On the leeward side the interfering ac- 
tion of wind-borne material, the prevalence of mild wave action 



CORRELATION OF THE MARINE AND FLUVIAL CYCLES 245 




w* 



246 DEVELOPMENT OF THE SHORE PROFILE 

because of offshore winds, and the existence of a landward in- 
stead of a seaward bottom current, would all tend to retard cliff 
recession. The absence of great storm waves in low latitudes, 
and the presence of coral building polyps, constitute special 
factors which would have to be taken into consideration in any 
attempt to compare shore development about tropical deserts 
with that about the more humid land areas of higher latitudes. 

Independence of Marine and Fluvial Cycles. — It is important 
to remember that there is no necessary connection between the 
stages of development of a shoreline and the stages of develop- 
ment of the land mass which it borders. Each one develops 
independently, the one under the influence of marine forces, 
the other under the influence of subaerial forces. If both begin 
their evolution at the same time, the shoreline may be young 
while the land mass is in a youthful stage of development; 
and it may even happen that both attain full maturity at 
about the same time. But this is not a necessary, and not 
even a common relation. When a young shoreline of submer- 
gence is produced by the partial submergence of a mature land 
mass, the land mass remains mature throughout the youth of 
the shoreline, for a slight submergence, which is sufficient to ini- 
tiate an entirely new cycle of shoreline development, produces 
scarcely any appreciable effect upon the main mass of the land. 
The sea invades the lower reaches of the valleys, and the remain- 
ing lower courses of some rivers may have their gradients slightly 
reduced if delta building takes place at the bay heads. But 
the land mass as a whole still consists of high hills and ridges 
separated by deep-cut branching streams; it is still a maturely 
dissected region, and its cycle of erosion continues without any 
real interruption toward the ultimate goal of planation. 

The principle here involved is an important one, and since 
there is not complete agreement concerning it, a further word of 
explanation is in order. Davis has at different times presented 
the idea that any change of level introduces a new cycle of land- 
mass development. According to his interpretation the land 
mass which was mature before depression had inaugurated a new 
cycle of shoreline development, would become young in a new 
cycle of subaerial erosion as soon as the change of level occurred. 
In speaking of such changes of level he writes, " The previous 
cycle (of land dissection) is thus cut short and a new cycle is 



INDEPENDENCE OF MARINE AND FLUVIAL CYCLES 247 

entered upon " 66 ; and again, " a cycle is interrupted when the 
land mass rises or sinks, or when it is warped, twisted, or broken. 
Like accidents, interruptions may happen at any stage of de- 
velopment. It is then convenient to say that the sequential 
form attained in the first incomplete cycle shall be called the 
initial form of the new cycle, into which the region enters, more 
or less tilted or deformed from its former shape" 67 . 

There are certain theoretical considerations which favor such 
an interpretation as is outlined in the above quotations; but it 
seems to the writer that numerous practical difficulties outweigh 
these considerations. Under the proposed scheme a submature 
plateau with large, flat-topped inter-stream areas, a mature 
plateau with sharp-crested ridges separated by V-shaped valleys, 
and an old plateau characterized by low and gently undulating 
topography, would all have to be called " young" in case each 
had been slightly depressed and not much modified since. Forms 
of totally different appearance, and typically characteristic of 
three distinct stages of normal plateau dissection, would be 
grouped together as in the same stage of development in the new 
cycle due to submergence. An observer in the interior would 
never be able to tell the stage of development of land forms until 
he had visited the coast to make sure that neither emergence nor 
submergence had introduced a new cycle, the recognizable effects 
of <which were limited to the coastal zone. Indeed, he would 
find that practically all land masses are young in the current 
cycle, for emergence or submergence has occurred on most 
coasts within a period geologically so recent that little modifi- 
cation of surface forms has occurred since. The terms young, 
mature, and old would no longer be aids to an appreciation of 
significant differences in land forms, and the strongest argument 
for interpreting the surface features of the earth in terms of 
their stages of development would disappear. Davis has him- 
self in a recent volume 68 recognized the difficulty of applying 
strictly his earlier suggestions regarding the terminology of the 
cycle and has proposed to avoid the difficulty in part by the use 
of circumlocutions or explanatory paraphrases. 

If it appears that I have pushed an unimportant point to an 
absurd extreme, it must be remembered that a substantial 
agreement as to the usage of the terms cycle, young, mature, and 
old is absolutely essential to an intelligent understanding of 



248 DEVELOPMENT OF THE SHORE PROFILE 

land form description, and that the difficulties I have portrayed 
are the necessary and logical consequence of considering every 
change of level as inaugurating a new cycle of land-mass develop- 
ment. If the same mountain mass is to be called mature by 
one observer because of the advanced stage of its dissection by 
stream erosion, and young by another observer who finds that 
its borders are slightly submerged in the sea, endless confusion 
must result. It will scarcely meet the situation to say that " a 
mature mountainous region was slightly submerged and is now 
young in the new cycle/' for such a double description is too 
cumbrous to supply the need for a concise, clear, and consistent 
method of land-form description. One may, however, properly 
say that " a mature mountainous region was slightly submerged, 
and its shoreline is now young." Every significant change of level 
does introduce a new cycle of shoreline development; and it is 
evident that failure to attach sufficient importance to the fact 
that the cycle of shoreline development and the cycle of land- 
mass development are wholly independent, and progress at differ- 
ent rates under the influence of different forces, is responsible 
for the conception that every change of level introduces a new 
cycle of subaerial denudation. The absence of a clear discrimi- 
nation between the two cycles Is especially noticeable in the con- 
text from which the second of the above quotations is taken 69 . 
""""All of the difficulties discussed above disappear if we adopt 
the following as fundamental principles in land-form description: 
(1) The cycle of shoreline development and the cycle of land- 
form development are measurably independent as regards the 
evolution of their sequential stages, and must be treated as two 
distinct cycles. Both may originate from the same change of 
level, their corresponding stages of development may in some 
instances be closely correlated especially near the sea, their 
relative rates of progress in a given region may be compared, 
and the influence of one upon the other may be studied; but 
the two distinct cycles must always be carefully discriminated. 
It might be added that the cycle of stream development, 
and the cycle of land-mass development (dissection) which are 
very generally confused with each other, as well as with the 
marine cycle, are likewise distinct and may progress at different 
rates 70 . (2) Emergence introduces a new cycle of shoreline devel- 
opment, and will, if of sufficient magnitude, introduce new cycles 



INDEPENDENCE OF MARINE AND FLUVIAL CYCLES 249 

of stream development and of land-mass dissection. A slight 
emergence, especially if very gradual, will merely accelerate the 
progressive development of the cycles of stream development 
and of land-mass dissection already current, or will, if re- 
peated, cause pulsations of reinvigorated stream cutting to 
advance inland up the rivers. The result may be minor topo- 
graphic changes of the highest importance to the student of 
past fluctuations of level, and these topographic records must be 
fully appreciated and emphasized. But unless they are of large 
magnitude, rising to the dignity of a truly rejuvenated topog- 
raphy, the short episodes which they represent should not be 
dignified by the name of cycles. (3) Submergence introduces 
a new cycle of shoreline development, but submergence alone 
never introduces a new cycle of stream development or of land- 
form dissection. This is because the forces which cause stream 
development and land-mass dissection continue their work as 
before, in essentially the same relative positions as before, even 
though absolute altitude is different and absolute efficiency may 
be more or less modified by a change in rainfall. Bayhead 
deltas may form in the drowned valleys, the gradients of some 
streams may be diminished for a limited distance inland from 
their mouths, and the rate of erosion on adjacent slopes may be 
somewhat retarded. But these local and temporary effects have 
no appreciable influence on the dissection of the land as a whole, 
and to no extent do they " rejuvenate " it. In other words, 
submergence does not " determine a more or less complete break 
in processes previously in operation, by beginning a new series of 
processes with respect to the new baselevel " n , and therefore does 
not inaugurate new cycles of stream or land-mass development. 
It is important that one should distinguish, not only between 
the shoreline cycle and other physiographic cycles, but also 
between stages in the development of the shore profile and stages 
of shoreline development. On a shoreline of submergence, for 
example, it very often happens that the shore profile at certain 
points becomes mature (i.e., the marine bench is pushed inland, 
the cliff weathers back to a gently inclined, soil-covered slope, 
and the shore profile of equilibrium is fully established) long 
before the shoreline as a whole is reduced to a comparatively 
simple line back of the bayheads. The shoreline in this case is 
still young, and may even retain the excessive irregularities of 



250 DEVELOPMENT OF THE SHORE PROFILE 

very early youth; but the shore profile is mature at some places, 
although still young at others. On the other hand, where wave 
erosion is unusually effective the irregularities of a shoreline of 
submergence may be quickly removed, and the shore outline 
transformed to a line of simple curvature back of the original 
positions of the bayheads, at a time when the waves are still 
actively undermining the marine cliffs and pushing them back- 
ward. In this case the shoreline is mature, but the shore pro- 
file is young. It would be quite proper to speak of that part of 
the profile called the marine cliff as a " young cliff," but to 
describe the shoreline as " young " would be erroneous. 

The coast of Normandy exhibits a shoreline of fairly simple 
curvature, bordered by very steep or even vertical cliffs of bare 
rock, from which landslides often descend into the rapidly ad- 
vancing sea. Here the shoreline is mature or late mature while 
the profile is young. Davis 72 has described the cliffs of this coast 
as late mature (" spatreife Kliffe "); but it is evident from his 
descriptions and from his characteristically expressive diagram 
representing this coast, that the expression " late mature " 
really applies to the shoreline alone, while the cliffs along the 
shoreline are marked by the steep slopes and frequent landslides 
found only in young cliffs. Davis has himself given such ex- 
cellent accounts of the diverse features of young and late mature 
marine cliffs in other connections that there can be no doubt his 
application of the term " late mature " to the Normandy cliffs 
was merely an oversight such as is common in physiographic 
literature where stages of shoreline development and stages of 
shore profile development are not sharply discriminated. 

Comparative Rapidity of Marine and Fluvial Planation. — 
Among those who admit the ability of unlimited wave action 
to reduce a land mass to an abrasion platform below sealevel, 
there are a number who believe that fluvial denudation takes 
place so much more rapidly, that any large land mass must 
be reduced to a peneplane before the waves could cut any 
great distance into the lands. This view is well expressed by 
Geikie 73 in these words: " Before the sea, advancing at the 
rate of ten feet in a century, could pare off more than a mere 
marginal strip of land, between 70 and 80 miles in breadth, the 
whole land might be washed into the ocean by atmospheric 
(meaning fluvial) denudation." 



RAPIDITY OF MARINE AND FLUVIAL PLANATION 251 

It is admittedly a difficult matter to find any basis for an 
adequate comparison of the relative rates of marine and fluvial 
denudation; but there should be no difficulty in seeing that 
Geikie's comparison is based on figures which enormously over- 
estimate the average rate of stream erosion. As a starting point 
in his calculations he takes the amount of sediment annually dis- 
charged by the Mississippi River, and computes that this river 
will lower the land throughout its whole drainage basin an average 
of 1 foot in 6000 years. He cites other rivers which reduce their 
drainage basins much more rapidly, but the rate just given is 
assumed as a conservative figure in calculating rates of fluvial 
denudation. The error consists in reckoning denudation at the 
same rate throughout the entire fluvial cycle. It is true Geikie 
recognizes that " the last stages in the demolition of a continent 
must be enormously slower than during earlier periods " 74 , but 
he makes no allowance for this fact in his calculations, except 
to intimate that the resulting error may be compensated for by 
the material removed in solution and not figured in the above 
estimate. 

The Mississippi River drains vast areas of high mountains and 
plateaus whose steep slopes contribute large quantities of waste 
to its upper branches; and extensive stretches of semi-arid 
plains where fine-grained unconsolidated sediment is shed into 
the streams with enormous rapidity. Much of the river's 
drainage area has reached maturity, and its larger branches are 
transporting heavy loads of debris on fairly steep profiles of 
equilibrium. There can be no comparison between the amount 
of material carried to the sea by the Mississippi at the present 
time, and the amount which will be carried when the mountains 
and plateaus are worn lower, the stream gradients reduced, the 
rainfall diminished because of decreasing relief, and the stream 
volumes greatly lessened because of decreased rainfall and in- 
creased evaporation. The annual denudation under those con- 
ditions will be but a very small fraction of what it is to-day, 
unless the efficiency of seolian denudation is enormously in- 
creased as the land wears lower. Instead of allowing 4,500,000 
years for the removal of the entire continent of North America, 
it is conceivable that it might be nearer the truth to allow that 
much time for the reduction of the surface by 1 meter during the 
latest stages of subaerial denudation. Portions of tertiary pcne- 



252 



DEVELOPMENT OF THE SHORE PROFILE 



o 

o 



PROBABILITY OF MARINE PLANATION 253 

planes which have been exposed to erosion for a period which 
may be estimated as one or more millions of years 75 , not only 
have not been reduced nearly to sealevel, but seem to stand 
somewhere near the original positions of the upland surfaces. 
Very many more millions of years would be required to reduce 
these areas of hard rock to a low-lying surface of fluvial denu- 
dation. How much this time might be shortened by seolian 
erosion is problematical; but the combined action of the sub- 
aerial forces could scarcely accomplish the work in so short a 
time as a few million years. 

It appears, therefore, that while it is not possible to more than 
guess at the time required for the subaerial denudation of a 
continent, the advantages are not so overwhelmingly in favor 
of subaerial denudation, and against marine denudation, as has 
been supposed to be the case. There are indeed, as we have 
already seen, certain marked advantages in favor of marine 
planation, not the least of which is the slight rise of sealevel, due 
to the infilling of sediment in the ocean basins and therefore nor- 
mal to the marine cycle, which brings the waves against the 
non-resistant fluvial deposits and residual hills of the old land 
mass. So far as a priori reasoning is concerned, we should 
recognize the possibility that wave erosion may completely 
plane away a large land area before the subaerial forces have had 
time to reduce it to sealevel. Which forces have been the more 
effective in producing known peneplanes must be decided, if at 
all, on the characteristics of the peneplanes themselves, and not 
on the basis of a priori arguments. 

Probability of Marine Planation. — Several authors have ex- 
pressed the opinion that movements of a land mass must prevent 
extensive marine planation by repeatedly forcing the waves to 
begin anew the cycle of denudation at a new level. This view 
is stated by Davis in the words: " The sensitiveness of a local 
shoreline to changes in the ocean basin or border all around the 
world makes extensive plains of marine abrasion of improbable 
occurrence " 76 . Emphasis is properly laid upon the fact that 
marine erosion is restricted to a narrow vertical zone about the 
margin of the lands, the position of this zone altering with every 
change in the relative level of land or sea; whereas subaerial 
denudation goes on simultaneously over the entire land area, 
regardless of sealevel oscillations. " A slight movement of 



254 DEVELOPMENT OF THE SHORE PROFILE 

elevation usually sets the sea back to begin its work anew on the 
seaward side of its previous shoreline, but such an elevation only 
accelerates the work of subaerial denudation all over the elevated 
region. The waves on the seashore shift their line of attack 
with every slight vertical movement of the coastal region; but 
the subaerial forces over large continental areas gain no notice 
of slight movements until a considerable time after they have 
been accomplished, and hence they perform their task only with 
reference to the average attitude of the land " 77 . 

When the theory of fluvial peneplanation was first proposed, 
it was objected that the land could not stand still long enough 
to permit streams to wear large areas nearly down to sealevel. 
The best answer to this objection was the finding of broad erosion 
surfaces, the characteristics of which indicated a fluvial origin. 
In like manner, we must depend upon field evidence to settle 
the question whether extensive planes or peneplanes of marine 
denudation have been produced in the past. We may fully 
recognize the sensitiveness of marine erosion to changes of level, 
without denying the possibility of marine planation. If we 
find erosion planes having the characteristics of planes of marine 
abrasion rather than those of subaerial denudation, we may 
reasonably conclude that the land can stand still long enough for 
waves to reduce a land mass to a plane surface. The distinguish- 
ing features of planes and peneplanes of different origins have 
been receiving more attention in recent years than formerly, 
and we may anticipate that discrimination between these sur- 
faces, at least where they are fairly well preserved, will become 
practicable. 

Attention may here be called to a' tendency to regard erosion 
surfaces which show characteristics of marine planation, as fluvial 
peneplanes which have been planed down further by the sea. 
It would perhaps be more pertinent to speak of them as marine 
planes or peneplanes whose development was favored by exten- 
sive subaerial erosion of the land. For when we remember that 
relatively flat fluvial peneplanes may have a relief of several 
hundred feet and that marine abrasion reduces a land mass many 
feet below sealevel, it is evident that the waves must perform 
much work in planing away a fluvial peneplane. Furthermore, 
marine abrasion destroys the essential characteristics of fluvial 
denudation, including the extensive adjustment of stream val- 



PROBABILITY OF MARINE PLANATION 



255 



X 




u 



tf 



. . ,. _ 



256 



DEVELOPMENT OF THE SHORE PROFILE 



a S 
^ .a 

£ o 



O O 



0) -~ 

8 >, 

to a; 

^ o 



^ a 



leys to weak rock belts, which is one of 
the best evidences of long-continued fluvial 
action. Since both marine and fluvial 
planation are possible, it is perhaps safer, 
in the absence of evidence to the contrary, 
to regard an erosion surface covered with 
remnants of a marine veneer as a marine 
plane or peneplane, rather than to make 
the gratuitous assumption that there must 
have been a fluvial peneplane which was 
later planed off by the waves. Rapid de- 
pression of a fluvial peneplane would econ- 
omize the amount of wave work necessary 
to produce the observed result 78 ; but one 
is not justified in assuming both fluvial 
peneplanation and rapid submergence in 
the absence of supporting evidence. 

It is sometimes assumed that a cover 
of marine sediments is an essential feature 
of a marine plane or peneplane 79 . While 
a thin marine veneer may be expected in 
many or even in most cases, its presence 
in any appreciable quantity does not seem 
necessary in the later stages of the marine 
cycle. A land mass reduced to an abrasion 
platform surrounded by a continental 
terrace, as a result of wave attack from 
all sides, would, in the penultimate stage, 
have the form of a very flat cone with 
the apex (a) where the last land surface 
was reduced (Fig. 40). Unimpeded by 
any further contributions of debris from 
a land area, wave erosion would proceed 
to remove the veneer which might have 
accumulated on the faintly conical plat- 
form, and to reduce the rock surface to 
waye base with no cover except an in- 
significant amount of recently eroded 
debris in transit to deeper water. As ex- 
plained on a previous page, the conti- 



ACCIDENTS DURING THE MARINE CYCLE 257 

nental shelf would then consist of deposited material at the outer 
borders, and a bare rock erosion surface within. Essentially 
the same conditions might prevail at an earlier stage, where a 
broad continental shelf bordered a still remaining land area, if 
the supply of land waste were very slow. When uplifted the 
land area, abrasion platform and continental terrace would 
occupy the same relative positions as the Older Appalachian 
Mountains, the Piedmont Belt, and the Atlantic Coastal Plain. 
A very thin marine veneer, quickly removed, might be insuffi- 
cient to superimpose rivers upon transverse hard rock ridges, 
even when these were worn down nearly to the level of an almost 
plane abrasion surface; and this partial initial adjustment of 
streams to rock structure would be greatly increased during 
further dissection. It is essential, therefore, to keep an open 
mind as to the possible origin of uplifted and dissected peneplanes 
which show no traces of a former marine cover, and which may 
even show a considerable adjustment of stream courses to rock 
structure. 

Interruptions and Accidents During the Marine Cycle. — 
Davis 80 has repeatedly emphasized the importance of the " in- 
terruptions " and " accidents " which frequently occur in the 
fluvial cycle. Similar events diversify the history of the marine 
cycle. We have already seen that elevation may end the prog- 
ress of the marine cycle at a given level by raising the abrasion 
platform and continental terrace, or parts of them, above the 
reach of the waves. Subsidence, if rapid, may produce the same 
effect by lowering the platform and terrace far beneath the 
lowest limits of wave activity. Slow, progressive subsidence 
may simply hasten the development of the marine cycle by 
constantly deepening the water offshore and thus facilitating 
wave erosion. It would seem, however, that any considerable 
help from subsidence would demand rather rapid sinking, in 
order to keep the water offshore continually and appreciably 
deeper. As subsidence progresses the inner margin of the con- 
tinental terrace advances landward, so that the outer margin of 
the abrasion platform is progressively overlapped by a wedge 
of marine deposits which thicken seaward (Fig. 41). 

Accidents may occur during any part of the marine cycle, and 
locally interfere for a time with the normal development of the 
shore profile. Glaciers may excavate deep troughs far below 



258 



DEVELOPMENT OF THE SHORE PROFILE 



wave base. Volcanic eruptions may build cones upon the con- 
tinental shelf, the summits of the cones possibly rising above 
sealevel. But in course of time the submarine troughs will be 
filled with sediment, the volcanoes will be removed by wave 
erosion, and the development of the shore profile will proceed 




Fig. 41. — Overlapping of marine deposits upon the abrasion platform of a 
slowly subsiding land mass. 

as before. A longer-enduring departure from the ideal scheme 
will occur if a strong and deep ocean current abrades the bottom 
long enough to reduce it below wave base. But even this ac- 
cident must be corrected as the removal of land masses and the 
reduction of shallows to wave base make concentrated current 
action impossible. 

SHORELINES OF EMERGENCE 

Initial Stage. — In the typical shoreline of emergence the 
water margin comes to rest against the exposed sea floor. Under 
normal conditions this floor consists of an abrasion platform 
and continental terrace, the smooth surface of which is inter- 
sected by the plane of the sea surface to form a very simple 
shoreline. Inland the land rises very gently in the form of a 







d^ 


c^--^ 










c 


9** 




B. ^ 


^ L 


g^~r ect 


b 


c 







Fig. 42. — Elements of the profile of a shoreline of emergence. 

smooth marine plane or coastal plain, as the case may be; sea- 
ward the bottom slopes downward with the same gentle incli- 
nation, giving shallow water for a long distance offshore. 

Davis has briefly outlined the broader features in the develop- 
ment of shorelines of emergence on the assumption that emer- 
gence is relatively rapid and is then followed by a still-stand of 
the land. Waves attack the initial shoreline with results to the 
profile which are at first similar to those produced at the shore- 
line of submergence. A marine bench (Fig. 42, b) is cut, a marine 



YOUNG STAGE 259 

cliff (c) produced, and a shoreface terrace (a) built. The bench 
may be covered by a thin beach deposit. But in two respects the 
development of the profile of a shoreline of emergence is signifi- 
cantly different from that previously described. In the first 
place, only small waves can reach the shore, because, according 
to the law of wave breaking set forth in Chapter I, large waves 
break when they enter water whose depth is approximately equiv- 
alent to the wave height; and this must occur well out from 
land in the case of shorelines of emergence. Accordingly, the 
marine bench is shallow, and the marine cliff is low, both being 
pushed slowly into a low lying plain by weak waves. Because 
of its insignificant size, the cut made by the waves during this 
earliest stage of development is often spoken of as a nip in the 
edge of the land. The nip is frequently preserved from further 
change for a long period of time by the development of an off- 
shore bar (B), which is a second feature characteristic of the 
shoreline of emergence, not found along typical shorelines of sub- 
mergence. 

As is elsewhere pointed out, it may well happen that pro- 
gressive emergence prevents the formation of a distinct nip on 
the mainland shore until after the offshore bar has been formed. 
If the levels of land and water then become stationary, and the 
lagoon is sufficiently broad and deep, lagoon waves may produce 
a nip of later date than the bar. On the other hand, if emergence 
continues, or if submergence intervenes, or if the lagoon waves 
are too feeble, the nip may be entirely lacking. Whether or not 
a nip is formed, the shoreline is past its initial stage and entered 
upon the stage of youth as soon as the offshore bar is built up 
above the water surface. 

Young Stage. — Under the various names of barrier beach, 
sand reef, and offshore barrier, the offshore bar has been described 
as a continuous narrow ridge of sand, lying some distance out 
from shore. Its seaward side has the normal beach profile of 
equilibrium, and its crest rises a few feet above high tide level. 

The precise manner in which the offshore bar originates is 
not definitely known. Various theories advanced to account 
for its development are considered at length in a later chapter 
but only two deserve special mention here. The first is that 
of Gilbert, which is based on the belief that the material of the bar 
consists of " shore drift," which is being moved parallel to the 



260 DEVELOPMENT OF THE SHORE PROFILE 

coast by longshore currents. " The most violent agitation of the 
water is along the line of breakers; and the shore drift, depending 
upon agitation for its transportation, follows the line of the 
breakers instead of the water margin. It is thus built into a con- 
tinuous outlying ridge at some distance from the water's edge." 81 
De Beaumont 82 would derive the material of the bar from the 
offshore deposits, by direct wave action. Davis, who follows de 
Beaumont, states the theory thus: " When waves roll in upon a 
shelving shore, much of their energy is expended on the bottom. 
Between the line of their first action far offshore and their final 
exhaustion on the coast, there must be somewhere a zone of maxi- 
mum action. This zone must lie farther seaward when large 
storm waves roll in than when the sea is slightly ruffled in fair 
weather. . . . Here the bottom is deepened; the coarser particles 
are moved landward, forming a shoal and in time a bar inclosing 
a lagoon; while the finer particles are moved seaward, where they 
are distributed in moderate thickness over a considerable area." 83 
Conformable to these two theories, Gilbert illustrates his idea of 
the offshore bar by a section which shows the bar deposit resting 
on the unbroken surface of an inclined sea-bottom; whereas in 
Davis's illustrations the sea-bottom is represented as deeply 
eroded by the waves which used the eroded materials to build 
the bar. In Gilbert's opinion the offshore bar is " absolutely de- 
pendent on shore drift for (its) existence. If the essential con- 
tinuous supply of moving detritus is cut off, . . . the structure 
(is) demolished by the waves which formed it " 84 . According to 
Davis, offshore bars " might be developed essentially under the 
control of on- and offshore action alone " 85 . 

Without pausing to discuss the relative merits of these two 
theories at this time, we may note that the further development 
of the shore profile would be essentially the same in either case. 
The profile of the seaward side of the bar is a profile of equilib- 
rium which varies with variations in the waves and other forces 
which affect the shore, in the manner already fully described. 
Beach materials are heaped upon the backshore (d) one day, and 
dragged out to form a shoreface terrace (a') the next. Vigorous 
wave action cuts into the sea-bottom to form a marine bench (b'), 
while the top of the bar or the sand dunes upon its crest may have 
a low but distinct marine cliff (c') marking the upper limit of 
the shore. 



YOUNG STAGE 261 

Normal development involves slow retrogression of the shore- 
line, as the grinding of the beach materials to fine silt permits 
their removal in suspension to deep water, or as seaward bottom 
currents drag coarser debris from the face of the bar down the 
inclined slope of the bottom toward the edge of the continental 
terrace. But the retrograding process does not necessarily in- 
volve the rapid removal of the bar. The material lost from the 
bar in the ways described above may be compensated for by 
material freshly cut from the sea-bottom during the landward 
cutting of the marine bench. Storm waves hurl debris over the 
crest of the bar to its back side, and the overwash of waves 
carries much additional material down its landward slope. 
Wind-blown sands still further assist this landward building. 
All these factors combined may be sufficient to build up the 
inner side of the bar as fast as the outer side is cut away, in 
which case the bar will retreat bodily toward the coast without 
any marked change in its average width. 

Between the offshore bar and the mainland lies a narrow strip 
of shallow water, called the lagoon (L), whose weak waves faintly 
cliff the lagoon shores, often at a lower level than the initial nip. 
Tidal currents bring fine sediments from the surf-beaten outer 
side of the bar, to deposit them in the quiet water of the lagoon, 
which also receives some stream-brought sediment from the lands, 
wind-blown sands from the beaches and dunes of the bar, and 
debris eroded from the lagoon shores by the waves. In course 
of time these sediments may build the floor of the lagoon up to 
such a level that salt marsh vegetation can take possession in the 
manner described by Shaler 86 in his oft-quoted paper on the " Sea 
Coast Swamps of the Eastern United States," and so transform 
the lagoon into a salt marsh. It must not be supposed, however, 
that all salt marshes back of offshore bars have had the history 
outlined by Shaler; for, as will be shown in a later chapter, the 
typical salt marshes of the Atlantic Coast have been formed in 
an entirely different manner. 

As the retrograding of the offshore bar continues, its sands and* 
gravels are driven in over the marsh surface. The enormous 
weight of the bar compresses the peat and other marsh deposits, 
which later outcrop on the seaward side of the bar near or below 
low-tide level, and thus bear witness to the retrograde move- 
ment of the outer shoreline. During all this movement the 



262 DEVELOPMENT OF THE SHORE PROFILE 

profile of equilibrium is maintained as perfectly as the varying 
conditions will permit. The bench is deepened as well as cut 
landward, and its seaward edge grades imperceptibly into a 
constantly broadening abrasion platform. Erosion products ac- 
cumulate in a continental terrace farther seaward. At length 
the bar is driven upon the mainland, the marsh or lagoon is ex- 
tinguished, and larger waves working on a steeper profile attack 
the coast where long before small waves on the gently sloping 
initial profile cut the less prominent nip. The shore profile is 
now thoroughly mature. 

i It is not necessary that the offshore bar should begin to retreat 
as soon as formed. Larger storm waves may build successive 
additional bars in deeper water on the seaward side of those 
formed earlier; but prograding of the shoreline from this cause 
can proceed to a very limited extent only, and the extensive 
series of " beach ridges " often attributed to this action must be 
explained in some other manner. One other explanation in- 
volves the supply of large volumes of debris by longshore cur- 
rents, which will cause long-continued prograding in the manner 
already explained for shorelines of submergence. If the long- 
shore currents supply just enough debris to make good the loss 
from wave erosion, attrition, and removal, the shoreline will 
remain stationary. 

Mature and Old Stages. — Whether or not the offshore bar 
is prograded for a period, retrograding must inevitably replace 
the temporary forward movement in the course of time, and 
the shoreline be driven back upon the mainland. Maturity 
begins when the lagoon or marsh is extinguished, and the waves 
have begun their real attack upon the coast. From this time 
on there are no features of shore profile development which 
differ in any essential respect from the mature and old profiles 
on shores of submergence. As both these stages of profile devel- 
opment have been fully discussed in connection with shorelines 
of submergence, we may dismiss them without further consid- 
eration. 

NEUTRAL SHORELINES 

The successive stages of development in the profiles of neutral 
shorelines involve little that is novel save in matters of detail. 
Marine erosion of delta shorelines, alluvial fan shorelines, and 



NEUTRAL SHORELINES 263 

outwash plain shorelines would give stages resembling those in 
the profile of shorelines of emergence, except that the offshore 
bar stage need not necessarily be represented in case the sea- 
ward portion of the profile descends too abruptly into deep 
water. 

The typical delta consists of two main portions, a subaerial 
plain and a subaqueous plain, separated by a steeper wave-cut 
slope to which Barrell 87 originally gave the name " shore face." 
The comparatively steep frontal slope of the delta may thus be 
far from the shoreline, as in the case of the Nile delta, and is 
unrelated to the true delta shore profile. The shoreface, on 
the other hand, is the steeper, landward portion of the shore 
profile of equilibrium, of which the profile of the gently sloping 
subaqueous plain is the seaward continuation. It should be 
noted that the outer margin of the subaqueous plain, where it 
joins the steeper frontal slope of the delta, does not mark the 
position of wave base, as most writers erroneously assume. It 
may mark the seaward end of the profile of equilibrium in any 
given section, the equilibrium referred to being the balance 
between the power of the waves on the one hand, and the work 
they must accomplish in transporting debris on the other. Stop 
the addition of sediment to the delta for a time, and the waves 
will slowly reduce the submarine plain, including its outer mar- 
gin, to a still lower level. Where the surface of the water 
body in which a delta is built has recently been raised or lowered, 
the outer margin of the subaqueous delta plain is not only 
unrelated to wave base, but is also unrelated as yet to the nor- 
mal profile of equilibrium for the new conditions. Wave base 
is an imaginary horizontal plane marking the lowest limit of 
effective wave erosion in a given water body. It is highly 
improbable that the seaward margin of any present day delta 
or shore terrace coincides with that imaginary plane, just as it 
is highly improbable that any present land surface coincides with 
the imaginary subaerial baselevel plane. 

Neutral volcano shorelines would have the same profile de- 
velopment as slopes of corresponding steepness on shorelines of 
submergence. Coral reef shorelines have one striking peculi- 
arity, in that they depend on organic as well as on inorganic 
forces for their history. Vigorous coral growth may indefi- 
nitely postpone the developmental stages of the reef under 



264 DEVELOPMENT OF THE SHORE PROFILE 

marine erosion, and may even for a long period build the reef 
forward into the sea despite the most vigorous wave attack. 

Fault shorelines deserve more than passing notice because of 
certain novel features which they present both in the initial and 
in later stages. If the hade of the fault plane is steep and the 
seaward block drops well below sealevel, in the initial stage 
the sea will come to rest against a steep cliff, the fault scarp 
(a}a 2 , Fig. 43) which descends abruptly into deep water. This 
initial stage may persist for an abnormally long period of time, 









/a* 


^yb-^p>^^__^^' 




„. Sealevel 












'■■■■■■:■: \-:-\-.\-:-y:<~&p:oot] 
/ 






^~"c^" 


-^^gr^g 


^^^»i 







Fig. 43. — Stages in the development of the shore profile of a fault coast. 

due to two important facts. In the first place, as we have 
already seen in an earlier chapter, waves approaching a vertical 
or nearly vertical wall rising out of deep water are reflected 
back without developing any great erosive power; and in the 
second place, where the water is deep close to shore the waves 
cannot arm themselves with any tools with which to facilitate 
their attack upon the land. Rock fragments weathering from 
the face of the cliff descend at once to deep water, beyond the 
reach of effective wave action. If the cliff is composed of very 
resistant rock which yields but slowly to the forces of weather- 
ing, the initial profile may long remain practically unaltered. 

In the course of time, weathering of the cliff face causes it to 
retreat and leads to the accumulation, at its base, of a submarine 
talus (6 1 )- Two important consequences follow. Wave reflec- 
tion is less perfect and hence the waves develop greater erosive 



COMPOUND SHORELINES 265 

power on the more sloping surface of the talus; at the same time 
the waves become armed with the talus debris, which is hurled 
against the cliff face with ever-increasing force. Under these 
favorable conditions the retrograding of the cliff face may be 
so accelerated as to give it a steeper slope (c 2 ) than it possessed 
a short time before (6 2 ), while the prograding of a true shoreface 
terrace (c 1 ) replaces the former talus growth. From this time 
forth the shore profile develops as in the case of shorelines of 
submergence. 

: COMPOUND SHORELINES 

The name " compound shoreline " has been applied to a shore- 
line which shows with more or less equal prominence features 
characteristic of at least two of the three simple classes of shore- 
lines. The best examples of compound shorelines exhibit the 
irregular pattern of drowned valleys in combination with a 
smooth and gently sloping sea-bottom from which an offshore 
bar usually rises to the surface. There is reason to believe that 
in such cases extensive emergence takes place first, and that later 
moderate submergence drowns the valleys carved in the emerged 
coast. Were submergence to occur first, it is probable that par- 
tial emergence soon after would find the sea-bottom still possessed 
of its former irregularities to such a degree that the new shoreline 
would still be a typical shoreline of submergence, with its essen- 
tial characteristics little affected by the uplift which operated 
merely to reduce the amount of submergence; whereas emergence 
a long time after would reveal a well-smoothed sea-bottom and 
give a typical shoreline of emergence. Compound shorelines, of 
which the North Carolina coast is a typical example, may there- 
fore be regarded as presumptive evidence in favor of emergence 
followed by partial submergence. 

The character of the initial profile of a compound shoreline 
of the North Carolina type will depend partly upon the amount 
of dissection which the emerged area experienced previous to 
the partial submergence, and partly upon where the profile is 
taken. If dissection was limited to areas adjacent to the main 
streams, and the profile is located so as to lie wholly in an undis- 
sected inter-stream area, it will not differ from the initial profile 
of the ordinary shoreline of emergence, providing no offshore bar 
has formed. When, however, an offshore bar forms before sub- 
mergence changes the shoreline to the compound type, and this 



266 DEVELOPMENT OF THE SHORE PROFILE 

bar is built up to the surface as submergence progresses, what 
may be called the initial profile of the compound shoreline will 
resemble the young profile of the shoreline of emergence, in 
which the bar is a prominent feature. If dissection was so 
extensive that submergence everywhere brings the water to 
rest against relatively steep valley sides, or if the profile is so 
located as to cross the shoreline of a slightly dissected and 
embayed plain within the limits of one of the drowned valleys, 
the initial profile of the compound shoreline will differ from the 
young profile of a normal shoreline of emergence in having a 
steeper slope at the water line, deeper water offshore, and a 
more irregular bottom for a limited distance seaward (Fig. 44). 




Fig. 44. — Profile of a shoreline of emergence when sealevel is at a, changed 
to profile of a compound shoreline when submergence brings the sealevel 
to b and facilitates the landward migration of the offshore bar. 

In case submergence is so rapid or so extensive as to destroy 
the original offshore bar, no new bar will form on the submerged 
irregular surface of the dissected land mass (unless the hills of 
the land were of such very moderate relief as to constitute prac- 
tically a level plain), and we will have a normal shoreline of sub- 
mergence instead of a compound shoreline. 

During submergence the offshore bar may be driven landward 
by the larger waves which are admitted by the deepening water 
offshore. The small waves in the lagoon will faintly cliff the 
lagoon shores, and currents will proceed to smooth out the in- 
equalities of the bottom by distributing the wave-eroded debris 
and the sediments brought in by tides and rivers. The further 
development of the shore profile will be similar to that of the 
ordinary shoreline of emergence. 

On a compound shoreline combining the features of a fault 
shoreline with those of a shoreline of submergence a profile 
through one of the drowned valley sections will have in general 
the same developmental history as the normal profile of a shore- 
line of submergence. A profile through a typical portion of the 
fault scarp will pass through the sequential stages already de- 
scribed for normal fault shorelines. 



RESUME 267 

RESUME 

We have now traced the history of the shore profile from its 
initial to its ultimate stage. The characteristics of the profile 
in all the different stages of development and in the several 
classes of shorelines have been fully considered, and shore profile 
development has been compared with the development of stream 
profiles. This study has led us to certain important conclusions, 
which must have an important bearing upon all investigations 
of marine erosion. Thus, it has been shown that a shore profile 
of equilibrium is early established, the maintenance of which is 
accompanied by constant loss of debris and consequent recession 
of the shoreline. The changes in this profile, which have given 
rise to so much misunderstanding on the part of many observers, 
are due to temporary changes in the balance of the shore forces, 
and are of small importance as compared with the general cycle 
of ^nore development. Of very great importance is the fact that 
long-continued wave action must reduce broad land areas to a 
plane, or at least to a peneplane, of marine denudation. We 
have found that such a plane or peneplane may be produced 
without progressive subsidence; that rapid wave cutting is no 
proof of a change in the relative level of land and sea: and that 
while subaerial denudation may temporarily embarrass marine 
abrasion by delivering much sediment to the sea margins, ulti- 
mate marine planation cannot thus be prevented. A compari- 
son of the relative rapidity of marine and fluvial planation indi- 
cates that the widespread opinion in favor of the greater efficiency 
of fluvial erosion rests upon an inadequate basis, and that marine 
forces may really be able to reduce a large land mass to a peneplane 
more rapidly than can stream erosion. Whether the land stands 
still long enough for such a result to be effected by the waves, is 
a question which cannot be answered on a -priori grounds and 
which depends upon careful and unprejudiced study of actual 
peneplanes for its solution. In prosecuting such study it is essen- 
tial to remember that neither the absence of marine sediments 
nor the presence of a certain degree of stream adjustment is 
conclusive evidence in favor of a subaerial as opposed to a marine 
origin for a given peneplane. The marine cycle of erosion is 
subject to interruptions and accidents, the occurrence of which 
does not, however, affect the general principles controlling the 
cycle of shore development under normal conditions. 



268 DEVELOPMENT OF THE SHORE PROFILE 



REFERENCES 

1. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

p. 700, Boston, 1909. 

2. Fennemen, N. M. Development of the Profile of Equilibrium of the 

Subaqueous Shore Terrace. Jour, of Geol. X, 1-32, 1902. 

3. Hunt, A. R. The Formation and Erosion of Beaches. Nature. XLV, 

415, 1892. 

4. Murray, John. [On movement of shingle in deep water.] In discus- 

sion of paper by John Coode, on Chesil Bank. Min. Proc. Inst. Civ. 
Eng. XII, 551, 1853. 
Murray, John. [On the effect of waves on breakwaters.] Min. Proc. 
Inst. Civ. Eng. XIX, 670, 1860. 

5. Fischer, Theobald. Fenomeni di Abrasione sulle Coste del Passi dell' 

Atlante. Rendiconti della R. Accademia dei Lincei, Rome. XVI, 
j 571, 1907. 

6. Kinahan, G, H. The Travelling of Sea-Beaches. Min. Proc. Inst. 

Civ. Eng. LVIII, 282, 1879. 

7. Hunt, A. R. On the Action of Waves on Sea-Beaches and Sea-Bottoms. 

Proc. Roy. Dublin Soc, N. S. IV, 282, 1884. 

8. Austen, R. A. C. On the Valley of the English Channel. Qua,rt. 

Journ. Geol. Soc. VI, 72, 1850. 

9. Shield, William. Principles and Practice of Harbor Construction, 

p. 75, London, 1895. 

10. Coode, John. Description of the Chesil Bank, with Remarks upon its 

Origin, the Causes which have Contributed to its Formation, and 
upon the Movement of Shingle Generally. Min. Proc. Inst. Civ. 
Eng. XII, 544, 1853. 

11. Wheeler, W. H. The Sea Coast: Destruction: Littoral Drift: Pro- 

tection, p. 17, London, 1902. 

12. Pendleton, A. G. [On the encroachment of the sea on the land on the 

south side of Long Island.] U. S. Coast Survey, Rept. for 1850, 
p. 81, 1851. 

13. Coode, John. Description of the Chesil Bank, with Remarks upon its 

Origin, the Causes which have Contributed to its Formation, and 
upon the Movement of Shingle Generally. Min. Proc. Inst. Civ. Eng. 
XII, 543, 1853. 

14. Fennemen, N. M. Development of the Profile of Equilibrium of the 

Subaqueous Shore Terrace. Jour, of Geol. X, 27, 1902. 

15. Wheeler, W. H. The Sea Coast: Destruction: Littoral Drift: Pro- 

tection, p. 5, London, 1902. 

16. Ibid., p. 34. 

17. Marindin, Henry L. On the Changes in the Ocean Shorelines of 

Nantucket Island, Massachusetts, from a Comparison of Surveys 
made in the Years 1846 to 1887 and in 1891. U. S. Coast Survey. 
Rept. for 1892, Pt. 2, p. 246, 1894. 

18. Johnson, Douglas W. and Reed, W. G. The Form of Nantasket 

Beach. Jour, of Geol. XVIII, 188, 1910. 



REFERENCES 269 

19. Otto, Theodor. Der Darss und Zingst Jahresb. der Geogr. Ges. 

Greifswald. XIII, 483, 1913. 

20. Johnson, Douglas W. Beach Cusps. Bull. Geol. Soc. Am. XXI, 

599-624, 1910. 

21. Fenneman, N. M. Development of the Profile of Equilibrium of the 

Subaqueous Shore Terrace. Jour, of Geol. X, 27, 1902. 

22. Vogt, J. H. L. Uber die Schrage Senkung und die Spatere Schrage 

Hebung des Landes im Nordlichen Norwegen. Reprint from Norsk 
Geologisk Tidsskrift. I, 18, 1907. 

23. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 177, 1899. 

24. Rankine, W. J. M. On Waves in Liquids. Philosophical Mag., 4th 

Ser. XXXVI, 55, 1868. 

25. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 175, 1899. 

26. Wright, W. B. On a Proglacial Shoreline in the Western Isles of Scot- 

land. Geol. Mag., N. S. Decade V, vol. VIII, 97-109, 1911. 

27. Lawson, A. C. The Post-Pliocene Diastrophism of the Coast of 

Southern California. Bull. Univ. of Cal. Dept. of Geol. 1, 115-160, 1893. 

Lawson, A. C. The Geology of Carmelo Bay. Bull. Univ. Cal. Dept. 
of Geol. I, 1-59, 1893. 

Lawson, A. C, The Geomorphogeny of the Coast of Northern Cali- 
fornia. Bull. Univ. Cal. Dept. of Geol. I, 241-272, 1894. 

28. Andrews, Edmund. The North American Lakes Considered as 

Chronometers of Post Glacial Time. Trans. Chicago Acad. Sci. 
II, 5-9, 1870. 

29. Fischer, Theobald. Fenomeni di Abrasione sulle Coste dei Paesi 

deh" Atlante. Rendiconti della R. Accademia dei Lincei, Rome. 
XVI, 573, 1907. 
"30. Fischer, Theobald. Kustenstudien und Reiseeindnicke aus Algerien. 
Zeit. der Ges. fur Erdkunde zu Berlin, pp. 554-576, 1906. 
-31. Fischer, Theobald. Kustenstudien aus Nordafrika. Pet. Geog. Mitt. 
XXXIII, 1-13, 33-44, 1887. 

- 32. Wharton, W. J. L. Foundations of Coral Atolls. Nature. LV, 392, 1897. 

33. Ibid., pp. 390-393. 

34. Daly, R. A. The Glacial-Control Theory of Coral Reefs. Proc. Amer. 

Acad. Arts and Sciences. LI, 157-251, 1915. 

- 35. Reusch, Hans. Strandfladen et nyt Track i Norges Geografi. Norges 

Geol. Unders., No. 14, 1-14, English summary, 144-145, 1893. 
—-Reusch, Hans. The Norway Coast Plain. Jour, of Geol. II, 347-349, 
1894. 
36. Richter, E. Die Norwegische Strandebene und ihre Entstehung. 
Globus. LXIX, 313-319, 1896. 

- 37. Vogt, J. H. L. Sondre Helgelands Morfologie. Norges Geol. Unders., 

No. 29, pp. 35-55, 1900. 
Vogt, J. H. L. Uber die Schrage Senkung und die Spatere Schrage 
Hebung des Landes im Nordlichen Norwegen. Reprint from Norsk 
Geologisk Tidsskrift. I, 8-22, 1907. 



270 DEVELOPMENT OF THE SHORE PROFILE 

38. Nansen, Fridtjof. The Bathymetrical Features of the North Polar 

Seas. The Norwegian North Polar Expedition. IV, Art. XIII, 231 
pp., 1904. 

39. Vogt, J. H. L. Sondre Helgelands Morfologi. Norges Geol. Unders., 

No. 29, p. 48, 1900. 

40. Nussbaum, F. Uber die Entstehung der Norwegischen Fjeldland- 

schaften, Fjorde, und Scharen. Mitt, naturf. Ges. Bern, 233-258, 
1909. 

41. Nansen, Fridtjof. The Bathymetrical Features of the North Polar 

Seas. The Norwegian North Polar Expedition. IV, Art. XIII, pp. 
20, 90, 1904. 

42. Cushing, S. W. The East Coast of India. Bull. Amer. Geog. Society. 

XLV, 87-88, 1913. 

43. Cushing, S. W. Personal communication. 

44. Nansen, Fridtjof. The Bathymetrical Features of the North Polar 

Seas. The Norwegian North Polar Expedition. IV, Art. XIII, pp. 
151-153, 193, 1904. 

45. Ibid., pp. 105-112. 

46. Ibid., p. 112. 

47. Richthofen, F. von. China. II, 768-773, Berlin, 1882. 

48. Richthofen, F. von. Fuhrer fur Forschungsreisende, p. 333, Hanover, 

1901. 

49. Martonne, E. de. Traite de Geographie Physique, p. 676, Paris, 

1909. 

50. Lapparent, A. de. Traite de Geologie; Phenomenes Actuels, p. 238, 

Paris, 1900. 
-51. Lapparent, A. de. Lecons de Geographie Physique, p. 263, Paris, 
1898. 

52. Kayser, Emanuel. Lehrbuch der Geologie. I, Pt. 4, 493, Stuttgart, 

1912. 

53. Scott, W. B. An Introduction to Geology, p. 171, New York, 1911. 

54. Hahn, F. G. Untersuchungen liber das Aufsteigen und Sinken der 

Kiisten, p. 23, Leipzig, 1879. 

55. Haage, Reinholde. Die Deutsche Nordseekiiste, p. 26, Leipzig, 1899. 

56. Ramsay, A. C. On the Denudation of South Wales and the Adjacent 

Counties of England. Mem. Geol. Surv. Great Britain. I, 327, 1846. 

57. Green, A. H. Physical Geology. 2nd Edition, p. 414, London, 1877. 

58. Jukes-Browne, A. J. Handbook of Physical Geology, pp. 182-183, 

London, 1892. 

59. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

p. 702, Boston, 1909. 

60. Gulliver, F. P Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 175, 1899. 

61. Fenneman, N. M. Development of the Profile of Equilibrium of the 

Subaqueous Shore Terrace. Jour, of Geol. X ; 1-32, 1902. 

62. Mitchell, Henry. On the Reclamation of Tide-lands and its Relation 

to Navigation. Report of U. S. Coast Survey for 1869. Appendix 5, 
pp. 85-86, 1872. 



REFERENCES 271 

- 63. Stevenson, Robert. On the Bed of the German Ocean or North Sea. 
Memoirs Wermerian Nat. Hist. Soc. Trans. III. 327, 1821. 

fa 64. Barrell, Joseph. Criteria for the Recognition of Ancient Delta De- 
posits. Bull. Amer. Geol. Soc. XXIII, 403-411, 1912. 

-<-65. Barrell, Joseph. Relative Geological Importance of Continental, Lit- 
toral, and Marine Sedimentation. Jour, of Geol. XIV, 318-319, 447- 
449, 1906. 

66. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

p. 285, Boston, 1909. 

67. Ibid., pp. 180-181. 

68. Davis, W. M. Die Erklarende Beschreibung der Landformen. 565 pp., 

Leipzig and Berlin, 1912. 

69. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

p. 181, Boston, 1909. 

70. Johnson, Douglas W. Youth, Maturity and Old Age of Topographic 

Forms. Bull. Amer. Geog. Soc. XXXVII, 649-650, 1905. 

71. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

p. 272, Boston, 1909. 

72. Davis, W. M. Die Erklarende Beschreibung der Landformen, p. 514, 
Leipzig and Berlin, 1912. 

73. Geike, A. Textbook of Geology. 4th Edition. I, 593, London, 1903. 

74. Ibid., p. 590. 

75. Williams, H. S. Geologic Biology, pp. 62-63, New York, 1895. 

76. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

p. 291, Boston, 1909. 

77. Ibid., p. 341. 

78. Ibid., p. 346. 

79. Ibid., pp. 340, 344. 

80. Ibid., 180, 272-276, 285, 289. 

81 . Gilbert, G. K. Lake Bonneville. U. S. Geol. Surv. Mon. I, 40, 1890. 

82. Beaumont, Elie de. Lecons de Geologie Pratique, pp. 223-252, 

Paris, 1845. 
83 „ Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 
p. 708, Boston, 1909. 

84. Gilbert, G. K. Lake Bonneville. U. S. Geol. Surv. Mon. I, 40, 1890. 

85. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

p. 710, Boston, 1909. 

86. Shaler, N. S. Preliminary Report on Sea-Coast Swamps of the Eastern 

United States. U. S. Geol. Surv. 6th Ann. Rept., p. 364, 1886. 

87. Barrell, Joseph. Criteria for the Recognition of Ancient Delta De- 

posits. Bull. Amer. Geol. Soc. XXIII, 385, 1912. 



^ - 



CHAPTER VI 
DEVELOPMENT OF THE SHORELINE 

A. SHORELINES OF SUBMERGENCE 

Advance Summary. — It is the purpose of the present chapter 
to trace the systematic development of the shoreline of submer- 
gence from its initial stage of extreme irregularity and complexity 
until it acquires the regular and simple outline characteristic of 
full maturity. The features of old age are reserved for attention 
in a later chapter. Special consideration is given to those ele- 
ments of shore form normally associated with the stages of youth 
and maturity, such as beaches, spits, bay bars, looped and flying 
bars, tombolos, cuspate bars and forelands, marsh bars, and bay 
deltas. The question as to whether it is desirable or practicable 
to recognize young, mature, and old stages of development of 
each of these particular forms is discussed, as is also the ques- 
tion as to which marine forces are principally concerned in their 
construction. The various forms discussed are illustrated by 
ideal diagrams and by maps of examples taken from nature. 

Initial Stage. — As was early hinted by de la Beche 1 , and 
later more clearly stated by Dana 2 , when a land mass is sub- 
merged the sea enters the main river valleys and their lower 
tributaries for a distance which depends upon the depth of 
submergence, comes to rest against the more or less steep slopes 
of adjacent hills or mountains, and overflows the lowest cols or 
passes which separate outlying hills from the higher main ridges 
or divides. The initial stage (Fig. 45) of the typical shoreline of 
submergence is therefore characterized by an exceedingly irreg- 
ular shoreline, many times longer than a straight line connecting 
two points on the shore; by numerous branching bays or 
drowned valleys in which comparatively deep water is found a 
short distance offshore; by many peninsulas projecting out to 
sea; by the presence of numerous islands; and by an irregular 
sea-bottom whose inequalities represent the former hills and val- 
leys of the land. Portions of the coast of Maine and of the 

272 



INITIAL STAGE 



273 



Chesapeake Bay region (Fig. 46) are bordered by shorelines of 
submergence, but little changed from the initial form, outside of 
which submarine hills and valleys are clearly shown by soundings. 
The great variety of form which initial shorelines of submer- 
gence may possess has already been suggested by the clas- 




Fig. 45. — Shoreline of submergence, initial stage. 

sification of shorelines outlined in Chapter IV. Such variety 
is inevitable, as will readily appear when we consider that 
everything which affects the shape of the land must also affect 
the form of the shoreline produced when the sea surface comes 
to rest against the land. A land mass may have a great variety 
of structures, which will be reflected in the shore forms. Those 
structures may be subjected to several different erosive processes, 
each of which produces surface forms peculiar to itself, and hence 
leaves its impress upon the shoreline of submergence. Each 
erosive process may be in any stage of its cycle when submer- 
gence occurs, and the resulting shore features will vary widely 
with the different stages of land form development. The stage 
of shoreline development reached at any given moment since 
submergence will, of course, profoundly affect the characteris- 
tics of the shore. 

It is essential, therefore, to a clear conception of the charac- 
teristic features of any shoreline that the description take ac- 
count of the structure of the land mass, the process or processes 



274 



DEVELOPMENT OF THE SHORELINE 




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YOUNG STAGE 



275 



by which the land mass has been eroded, the stage of land mass 
dissection reached when submergence occurred, and the stage 
of shoreline development reached since submergence. To say 
that " the coast of Dalmatia represents a region of folded 
mountains, maturely dissected into longitudinal ridges and val- 
leys by normal stream erosion, and then slightly depressed to 
form a shoreline of submergence which is now in the youthful 
stage of its development, " will bring to the hearer who is familiar 
with the elementary principles of shoreline development a clearer 
mental picture of the essential characteristics of that shoreline 
than could a much longer and more detailed account of indi- 
vidual bays, peninsulas, islands, and other local features. 
Greater definiteness may be given to the mental picture if the ex- 
planatory description quoted above is made to include a statement 




Fig. 47. — Early youth of a shoreline of submergence, showing crenulate 

shoreline. 



as to the relief and texture of the topography produced by 
stream erosion; for the coast will be bold or subdued according 
as the relief is high or low, and the bays will branch moder- 
ately or intricately according as the texture is coarse or fine. 

Young Stage. — As rapidly as submergence brings the hill 
and valley slopes within reach of the sea, waves attack those 
slopes. We have already seen that in the early stages of wave 
attack the cliff profile is more irregular than in the initial stage , 




Bolus Head 



Fig. 48. — Crenulate shoreline of the southwest coast of Ireland. 

Page 276 



YOUNG STAGE 



277 




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278 



DEVELOPMENT OF THE SHORELINE 



because resistant and non-resistant rocks are unequally affected 
by wave erosion. In a similar manner the initial shoreline is 
rapidly made extremely irregular, on a small scale, wherever 
the land presents to the sea rocks of unequal resistance. The 
hills and valleys of the land may have been well graded and 
characterized by smooth, flowing contours, in which case the 
initial shoreline must be composed of well-rounded curves. 

But early in the youth 



of the shoreline the 
curves will be changed 
to sharply and irregu- 
larly crenulate lines 
by differential wave 
erosion 3 (Fig. 47). In 
other words, although 
the ultimate goal of 



M.Aka-caku 




kau-caku 



wave erosion is to 
make a shoreline of 
submergence less 
irregular, as will pres- 
ently appear, the first 
effect is to make it 
minutely more irreg- 
ular. We may call a 
shoreline of this char- 
acter a crenulate shore- 
line. The shoreline 
of southwestern Ire- 
land (Fig. 48), border- 
ing the beautifully 
graded hills of a ma- 
turely dissected and 
partially submerged land area, is in this crenulate stage of de- 
velopment, as may readily be observed from the deck of a 
transatlantic steamer passing near the coast on its way to 
Liverpool. Portions of the coast of Japan (Fig. 49) likewise 
afford excellent examples of crenulate shorelines. 

During early youth some of the most picturesque features of 
cliff detail begin to appear. On rocky shores isolated pinnacles 
of resistant material are left standing for a time in front of 



Fig. 49. — Young shoreline of submergence near 
Idzuhara, Japan, showing crenulate stage. 
(From Russian map based on Japanese data.) 



YOUNG STAGE 



279 




280 



DEVELOPMENT OF THE SHORELINE 

Plate XXXVI. 




Fingal's Cave on the island ot Staff a, Scotland. A sea cave formed by 
wave erosion in columnar basalt. 



YOUNG STAGE 281 

the main cliff. These chimneys or stacks (Plates XXXIV and 
XXXV) may be sculptured by the waves into very "striking 
forms. Weaker zones are excavated by the waves into sea caves 
(Plates XXXVI and XXXVII), of which Fingal's Cave on the 
island of Staff a is a well-known example. Where a projecting 
belt of rock is completely pierced by the wave attack, an arch 
(Plate XXXVIII) is formed. In front of the cliff low tide may 
expose a bare rock platform representing the landward edge of 
the marine bench upon which the occasional stacks are situated 
(Plates XXII and XXVIII). From the face of the cliff numer- 
ous landslides (Plate XXXIX), usually small but sometimes of 
grand dimensions, are precipitated into the water or upon the 
rock platform as a consequence of the rapid encroachment of 
the waves along the cliff base. It should be noted that while 
the above-named features begin to appear in the early youth of 
the shoreline of submergence, and reach their most abundant 
development before maturity is attained, they may.also be present 
on fully mature shores. 

Because of wave refraction, the seaward ends or " headlands " 
(Plate XXXIII) of peninsulas and islands are more vigorously 
attacked than other parts of the shore, while the inner ends of 
the bays, or " bay heads," suffer least. In a comparatively 
short time, therefore, there are developed cliffed headlands of 
striking aspect (Fig. 50, ch) . Part of the material eroded from 
the headlands is deposited in the depressions of the irregular 
seafloor, a second part is carried out to the deep sea, while a 
third part is temporarily built into various types of beaches 
and embankments. 

The great variety of forms assumed by these beaches and 
embankments is dependent upon the unorganized condition 4 of 
the longshore currents near a young shoreline of submergence, 
and distinguishes the latter from all other classes and stages of 
shorelines, which are much more simple. As shown by Figure 
51, tidal currents are broken up and deflected in various direc- 
tions by the sinuosities of peninsulas, islands, and drowned 
valleys, whenever they impinge upon an irregular coast. Beach 
drifting under the influence of the swell and of direct wind waves 
will be equally irregular, and will often be opposed to the direc- 
tion of tidal currents. The complexity will be increased wherever 
other types of currents are disintegrated against the irregular 



282 



DEVELOPMENT OF THE SHORELINE 




YOUNG STAGE 283 

shore. Eddy currents are unusually numerous along ' such a 
coast. Wave-eroded debris which is moved by any of these 
currents must accordingly be built into an almost endless variety 
of isolated forms not intimately related to each other. 

Beaches. — In early youth no very extensive beach is apt to 
form at the base of the headland cliffs, although narrow headland 
beaches (Fig. 50, hb) may be found in favored localities, especially 
if the cliff is composed of non-resistant sand or other material 




FlG. 50. — Young shoreline of submergence, showing types of beaches, 
bars, spits, and forelands. 

which readily disintegrates. Most of the debris, however, is 
swept from the marine bench at the base of the exposed cliff 
as rapidly as erosion and weathering remove it from the cliff 
face. Beach drifting, possibly aided by other types of longshore 
current action, propel a considerable portion of the debris along 
the shores of the bays toward the bay heads. These latter areas 
are loci of deposition because wave refraction has here reduced 
wave erosion to a minimum, because beach drifting due to on- 
shore wind waves and to the swell is far more potent than any 
beach drifting which can result from offshore winds, because direct 
wind currents moving from the ocean surface into the bays are 
more effective than wind currents originating at the heads of the 
bays and moving seaward, and because flood-tide currents fol- 
lowing the shores of a narrowing bay are apt to be more power- 



284 



DEVELOPMENT OF THE SHORELINE 







YOUNG STAGE 



285 



ful than the opposing ebb currents. It happens, therefore, that 
much of the debris eroded from the headlands is built into bay- 
head beaches (bh) at the inner ends of adjacent bays (Plate XL). 
The material in transit along the sides of the bay may form bay- 
side beaches (bs) which when fully developed connect the usually 
unimportant headland beaches with the more often well-devel- 
oped bay-head beaches. 

Embankments. — As may be observed from Figure 51, the shore 
currents of a young shoreline of submergence sometimes pass 







Fig. 51. — Initial unorganized condition of currents along a young shoreline 
of submergence (left hand figure) compared with organized condition 
which obtains when the stages of submaturity or maturity are reached 
(right hand figure). Light arrows = longshore currents, heavy arrows 
= offshore currents. 



directly across the mouths of subsidiary bays instead of closely fol- 
lowing the trend of the shore; or an offshore current, such as a 
planetary or large eddy current, may keep its course past the outer 
headlands but little influenced by the bays. Under these condi- 
tions the shore debris may be built out into the water in the form 
of a narrow embankment which grows by an excess of deposition 
at its seaward terminus, just as a railroad embankment is extended 



286 



DEVELOPMENT OF THE SHORELINE 



d 








YOUNG STAGE 



287 



by the dumping of car-loads of debris at its free end 5 . In the 
case of the current-built embankment, deposition takes place 
partly because the current, which is comparatively swift where 
it impinges against the headland or the already completed por- 
tion of the embankment and therefore able to transport a large 
amount of debris, loses part of its velocity when it passes into 
the deeper, open water off the bay mouth; and partly because 
the debris, as soon as it reaches deeper water, is no longer 
effectively agitated by normal wave action which in shallow 
water served to raise it 
intermittently into the 
moving water of the cur- 
rent. The seaward side 
of the narrow embank- 
ment is acted upon by the 
ocean waves, which build 
its crest above normal sea- 
level and establish a pro- 
file of equilibrium, similar 
to that of an ordinary 
beach (Fig. 36). The 
quiet-water side may have 
a more uniform slope, de- 
termined by the subaque- 
ous angle of repose of the 
deposited material. If 
the debris is coarse, the 
distal end of the embank- 
ment will have an abrupt 
slope to deep water, which 
also represents the subaqueous angle of repose of the material 
composing the embankment; but if the debris is fine, deposition 
will be less sudden, and the distal end will slope more gradually 
into deep water. 

Spits. — • So long as an embankment has its distal end termi- 
nating in open water, it is called spit (Fig. 50, s. See also Figs. 
52 and 53) . When the spit first begins to develop the longshore 
current responsible for it is normally so effective in comparison 
with other currents that the latter have little or no effect upon 
its form. Tidal currents may pass in and out of a bay at right 




Fig. 52. — Sand spits on the shore of 
Port Orchard, Washington. 



288 



DEVELOPMENT OF THE SHORELINE 




■3 

aa 
ft 

a 



-a 

93 



1 


■ 1 \ 

m 

ILJk J 





YOUNG STAGE 



289 



angles to the spit's direction of advance, or beach drifting may, 
under the influence of onshore winds, tend to drive the debris at 
the terminus into the bay; but deposition by the dominant long- 
shore current lengthens the spit so rapidly in the direction of 
that current's intention that the weak or intermittent efforts of 
contrary currents produce no sensible effect. With the continued 
growth of the spit, however, 
and the consequent narrow- 
ing of the entrance to the bay, 
tidal currents pass the end of 
the spit with an ever-increas- 
ing velocity. More and more 
of the debris brought by the 
longshore current is carried in 
toward the bay by the flood 
tide, thus giving a landward 
deflection to the embankment. 
Outflowing currents sweep 
some of the debris seaward, 
but the combined effects of 
the longshore current and 
active wave erosion normally 
prevent any marked seaward 
deflection. The longshore 
current may itself be deflected 
toward the bay by the flood 
tide, thus assisting in the land- 
ward deflection of the spit 
it is building. Furthermore, 
when the spit first begins to 
grow, its elongation proceeds 
with comparative rapidity, 
because the water is shallow 




Fig. 53.. — Simple spit (below) and 
compound recurved spit (above) at 
entrance to Port Moller, Alaska. 



and no great amount of debris is necessary to build the em- 
bankment up to the surface. But as it advances into deeper 
water, more and more of the debris must be laid down in the 
depths, and less and less is available for the linear extension of 
the spit. Under the new conditions of slow advance the influ- 
ence of flood tide and of beach drifting due to onshore winds 
becomes increasingly apparent, the debris at the terminus is 






290 DEVELOPMENT OF THE SHORELINE 

carried farther landward before new supplies are laid down in 
front of it, and a landward deflection of the spit results. Under 
these and other similar conditions it often happens that the 
end of a spit is more or less strongly curved inward. When 
the growing embankment acquires this form it is called a hooked 
spit, or better, a recurved spit (Fig. 50, rs). 

The forces supplying debris to the longshore current, the 
longshore current itself, and the contrary currents which tend 
to recurve the spit, do not always act with even approximate 
uniformity. One or more of these activities may have a very 
pronounced intermittent character. In such a case, the forces 
tending to elongate the spit in a straight or slightly curved 
line may prevail for a period, after which the forces operating 
to recurve the spit may temporarily gain the ascendancy. The 
effect of this intermittent action will be to produce a spit whose 
inner side is diversified by a series of landward deflected points 
representing successive recurved termini. To this interesting 
form the name compound recurved spit (Fig. 50, crs) may be 
applied. 

It sometimes happens that after a recurved spit is formed, 
new currents arise which remove material eroded from the 
more protected parts (usually the inner side) of the spit, and 
build it into a new embankment which is really essentially in- 
dependent of the form from which it projects. The original 
and secondary spits do not curve or merge into each other; 
on the contrary their lines of growth intersect at distinct angles, 
indicating their independent relationship. The secondary spit 
is no more an integral part of the original spit than the latter 
is an integral part of the cliffed headland from which it springs. 
Since it is desirable to give the combined spits a single name be- 
cause of their association in nature, we may speak of the grouped 
features as a complex spit (Fig. 50, cs). Sandy Hook is an 
excellent example of a compound and complex recurved spit. 
The landward curvature of successive termini is clearly indi- 
cated by the contours on the Sandy Hook topographic quad- 
rangle. But the southwardly deflected embankments which 
have generally been regarded as representing merely an extreme 
amount of recurving of the original spit are seen on closer 
examination to be independent secondary spits built by the 
waves and currents of Sandy Hook Bay with material eroded 



YOUNG STAGE 291 

from the northwesterly trending embankments of the original 
form (Fig. 57). 

Occasionally it happens that variable or periodically shifting 
currents extend a spit first in one direction, then in another, 
giving to it a more or less serpentine pattern. To this compara- 
tively rare form the name serpentine spit may be applied. Gul- 
liver 6 mentions two examples of this type in his essay on 
" Shoreline Topography." 

As the cliff from which a spit springs is cut back by the waves, 




/V/''/ 



j#i';S 

VK>— N *- 



Fig. 54. — Successive stages in the development of one type of compound 

recurved spit. 

the spit itself is driven landward at the same rate. This retreat 
of the shore leads to several interesting results, as will readily 
appear from Figure 54. If aa' is the original position of the spit, 
and the cutting back of the cliff causes the point of its tangency 
with the mainland to migrate toward the left, then the spit will 
assume the several positions indicated until it arrives at bb f . 
As will be observed, the spit may thus acquire a compound 
form with a succession of recurved points on its inner side, 
without necessarily experiencing any extension of its absolute 



292 DEVELOPMENT OF THE SHORELINE 

length. It should be noted, furthermore, that the progressive 
increase in the length of the ancient points does not in this case 
indicate a progressive increase in the relative strength of the 
landward moving currents, as has been generally assumed ia 
such cases. 

The marked angle at which the present shore intersects the 
axes of the ancient recurved points is evidence of their genetic 
relation to a former seaward position of the spit. This angle is 
normally greatest in the case of the oldest points, and decreases 
progressively in those which are of more recent date ; but increas- 
ing effectiveness of landward moving currents may sometimes 
cause the latest points to bend landward at increasingly greater 
angles. Should the spit increase in length at the same time that 
it is pushed back, we may have a case in which the compound 
feature is observable only in the distal portion, the landward 
end being a simple, straight embankment (Fig. 55). This does 
not mean that the two unlike parts of the spit have had different 
histories, but merely that the landward end has been pushed 
completely back of the termini of the recurved points which for- 
merly existed seaward of it. 

The characteristics of a retreating compound spit are well 
seen in the embankment which encloses the harbor of Toronto 
on Lake Ontario. Figure 55, based on charts by Hind, 7 ex- 
hibits a compound distal portion, where an admirable series of 
recurved points are separated by subparallel ponds or lagoons, 
and a simple landward portion which has been pushed back 
beyond the position of the corresponding points in that region. 
The greater length of the remaining portions of the more recently 
formed points, and the greater angle which the oldest points 
make with the present shore, are well shown. Judging from 
the charts the ends of the recurved points are truncated by 
subordinate spits, which give the whole a more complex form 
than it would otherwise have. In 1854 Sanford Fleming 8 pub- 
lished an excellent essay on the history of this interesting shore 
form, clearly setting forth the essential stages of its development 
previous to the time of his study, and predicting probable 
future changes. 

In the case just mentioned both the mainland cliff and the spit 
have retreated landward. There are cases in which the cliff 
beyond the base of the spit is cut back much more rapidly 




Page 293 



294 



DEVELOPMENT OF THE SHORELINE 



than at the point of attachment, while the spit as a whole ad- 
vances seaward instead of retreating. Thus, in Figure 56, where 
a former spit (E) springs from the cliff base at the point B, the 
cliff southeast of this point is cut back very rapidly, while to the 
northwest there is little or no cliff erosion and the mainland is 
being protected by the growing spit. The cutting back of the 




Fig. 56. — Development of the Cape Cod shoreline (after Davis). As the 
shore facing the Atlantic Ocean is cut back toward the west (A, C, D) the 
Provincetown sand spit grows progressively seaward (E, G, J), and the 
fulcrum point near B shifts from F 1 to F s . 



cliff at the southeast produces two important results: First, the 
direction of the shoreline is changed, so that the longshore cur- 
rent responsible for the spit comes from a more southerly direc- 
tion and hence tends to maintain its course more toward the 
north after it passes B ; in the second place, the cutting back of 
the shore removes the many irregularities which formerly disin- 
tegrated the currents impinging upon them, a single vigorous 
current along the simple shoreline replaces the many weak ones 
which flowed here and there along the complex shoreline, and 
this more vigorous current will maintain its more northerly course 
into open water after passing the point B because there is no 



i 



YOUNG STAGE 295 

force competent to deflect it into the bay as readily as the origi- 
nal weaker currents were deflected. As a result of these condi- 
tions, the axis of spit-building moves progressively seaward, as 
the cliff to the south is pushed progressively landward. Near 
the point B there is a " fulcrum " (F), north of which the shore- 
line is everywhere prograded, while south of it there is only 
retrograding. As Davis has shown in his classic essay on 
" The Outline of Cape Cod," 9 which contains the first adequate 
presentation of the fulcrum idea, the fact that some erosion is 
experienced at the point B and on the adjoining base of the spit 
causes the fulcrum point to shift slightly in the direction of 
the spit from F 2 to F 3 in Fig. 56. (See also Fig. 57). The 
Provincelands of Cape Cod and Sandy Hook are both good 
examples of spits formed in the manner above described. In 
the case of Sandy Hook the position of the earliest part of the 
spit, corresponding to E of Figure 56, may be indicated by the low 
sandy beach plain on the northeast side of Navesink Highlands, 
while Island Beach represents the remnant of a later addition 
to the spit. Sandy Hook itself advanced to the north and east 
by the successive additions of recurved points, as the shore near 
Long Branch was driven back toward the west. The fact that 
the base of Sandy Hook spit connects with a bay bar at the 
present time, instead of with the cliff on the east end of the 
Highlands, introduces a slight complication. 

Johnson and Reed have shown that in so complex a 
series of spits and bars as that composing Nantasket Beach 
on the Massachusetts coast, the phenomenon of a shifting 
fulcrum between a retrograding cliff and a prograding beach 
plain may occupy an important place in the history of the 
shoreline 10 . 

It has already been shown that the distal portion of a spit, 
and consequently of each recurved point representing a former 
distal portion, is submerged, the end of the embankment sloping 
down into deep water either abruptly or gradually according 
to the nature of the debris of which it is constructed. The 
super-aqueous portion owes its height primarily to. the waves, 
but in the case of sand spits wind action may locally raise the 
level a number of feet by forming dunes. Disregarding the dis- 
turbing effect of the wind, the height of a spit will depend upon 
the exposure to wave action; big waves will cast the debris 




Fig. 57. — Development of Sandy Hook spit. As the original shore between Sea- 
bright and Long Branch was cut back by wave attack, the zone of spit forma- 
tion north of Navesink Highlands advanced toward the northeast. The fulcrum 
point, dividing the zone of retrograding shoreline from that of prograding shore- 
line, shifted progressively from F l to F*. West of the letters "oo" in "Hook" 
is a small southward-pointing spit built by waves from the northwest out of 
material eroded from the recurved points of the main spit. 
Page 29G 



YOUNG STAGE 297 

many feet above mean water level, while small waves will 
raise the surface but slightly above the lake or sea. Since 
the exposure of a recurved spit to wave action is unequal, it 
follows that some portions must be higher than others; and it 
is normally the case that the distal curved portion, which is 
acted upon by the smaller waves of the bay into which it is 
being deflected, has a distinctly lower crest line than the rest 
of the spit. The importance of a proper appreciation of this 
simple relation will appear when one remembers that the low 
altitude of the crests of the recurved points in a compound spit 
have erroneously been regarded by some observers as a proof of 
coastal subsidence. 

The successive embankments added to a growing compound 
spit may be closely spaced, with shallow depressions between 
them whose bottoms do not extend as low as sealevel; or the 
embankments may be widely spaced and separated by lagoons 
of fairly deep water. If the supply of debris, longshore current 
action, and the activity of other currents are fairly uniform and 
constant, the successive embankments will be closely spaced 
and tend to form a continuous plain, which we may call a beach 
plain in view of the fact that it is composed of beach deposits 
cast up by the waves. It very seldom happens that all forces 
operating at the shore are so uniform and continuous as to give 
a perfectly smooth plain surface; on the contrary, the surface 
of the beach plain ordinarily shows a series of low ridges repre- 
senting the crests of beaches built by the waves along successive 
positions of the shoreline. These beach ridges, or " fulls " as 
the English geologists call them, constitute lines of growth of 
the beach plain, and when well preserved enable one to trace 
the history of development with great accuracy. They vary in 
altitude according to exposure to wave attack, but from three 
to twenty feet above ordinary high water level may be taken 
as the more common elevations. Beach ridges are conspicuous 
features of certain other coastal forms besides spits, and will be 
further considered when those forms are described. 

If any one or more of the forces involved in spit building 
operate very irregularly or intermittently, it may happen that 
successive embankments will be built at wide intervals. Let us 
imagine that the longshore current runs much more swiftly at 
rare intervals than at other times. For a long period it may 



298 DEVELOPMENT OF THE SHORELINE 

flow too slowly to remove all of the debris eroded from the 
cliff, and a large beach deposit accumulates at the cliff base 
and along adjacent parts of the spit. During this time such 
material as the current does transport is easily carried around 
the recurved point and in toward the bay, because the landward 
directed currents are competent either to move the load of a 
comparatively weak longshore current back to the previously 
established shoreline, or to deflect the longshore current itself 
so that it deposits its load directly along that shoreline. Now 
let us suppose that the longshore current is accelerated. Its 
increased velocity will enable it to pick up and transport the 
large load of debris which accumulated during its period of 
sluggishness; and will also impel the current to maintain its 
course straight ahead into deep water, instead of suffering de- 
flection into the bay when it reaches the recurved point of the 
spit. Furthermore, the shore below the fulcrum has been cut 
back to some extent during the period since the last recurved 
point was formed; and while the effect of this was not readily 
apparent so long as the longshore current was comparatively 
sluggish, a vigorous current finds at once that the prolongation 
of its normal course lies to seaward of the distal part of the 
spit. Large quantities of debris, borne by a current which de- 
parts from the former shoreline and advances into open water, 
must be built into an embankment which elongates rapidly in the 
direction of current advance. Waves raise the surface of the new 
embankment into a beach ridge; and by repetitions of this proc- 
ess there are formed successive beach ridges separated by lagoons 
of considerable breadth. Irregular or intermittent activity of 
other shore processes may produce the same result. 

Ordinarily the intermittent character of shore activities is 
not sufficiently pronounced to cause the building of new em- 
bankments so far removed from the older ones as to have really 
deep water between them. Usually a shallow lagoon or merely 
a marshy swale separates the ridges. The compound recurved 
spit at Toronto has a series of elongated ponds of shallow depth 
(Fig. 55), as has also the compound recurved spit known as 
Presque Isle on the south shore of Lake Erie (Fig. 58). Sandy 
Hook exhibits close-set ridges, or ridges separated by shallow, 
marshy swales. It is possible that in the latter spit the channels 
northeast and southwest of Island Beach (Fig. 57) occupy the 



YOUNG STAGE - 299 

positions of lagoons or bays between former ridges now largely 
destroyed. 

The ultimate length of a spit is attained when the tendency 
of longshore transportation to increase that length is just bal- 
anced by the opposite tendency of contrary currents. Where 




Fig. 58. — Lagoons and ridges of the Presque Isle compound recurved spit 

the embankment is extending across a bay, progressive length- 
ening narrows the inlet through which tidal, hydraulic, and 
other currents must pass in and out, and thus increases the 
velocity of those currents. This process continues until the veloc- 
ity of the latter currents is just high enough to counteract the 
constructive tendency of the longshore currents, when the em- 
bankment ceases to grow. The point of equilibrium is the sooner 
reached because wave action on the seaward side of the embank- 
ment continually reduces the size of the particles in transit, with 
the result that the farther the spit advances into open water 
the less powerful are the cross currents required to remove 
material from its distal end. Recurved points build into the 
bay until a similar condition of equilibrium is established be- 



300 



DEVELOPMENT OF THE SHORELINE 




Fig. 59. 



tween the currents tending to lengthen and those tending to 
remove the point. Because of the varying intensity of all 
shore processes, the equilibrium is never perfect, but only approxi- 
mate; and the end of the embankment therefore advances and 

retreats intermittently over a narrow 
zone which might be called the " zone 
of equilibrium." It is believed by 
some that Sandy Hook has reached 
this zone of equilibrium, and that the 
currents into and out of New York 
Bay are now sufficiently strong to 
overcome the efforts of the north- 
ward flowing longshore current to 
increase the length of the spit. This 
view is expressed by Duane 11 in the 
following words: " It (Sandy Hook 
spit) appears to have reached a limit- 
ing length at which the currents into and out of New York Bay 
have sufficient strength to scour away sand deposited at its 
northern end, and in the last one hundred and forty-five years 
its length has varied only about 2700 feet, sometimes increas- 
ing and sometimes decreasing." 

Bay Bars. — If the zone of 
equilibrium is not reached by 
the embankment until it has 
almost closed the inlet, or if 
the longshore currents prevail 
throughout and succeed in ex- 
tending the embankment com- 
pletely across the bay, the spit 
becomes a bay bar. A spit may 
thus change to a bay bar inter- 
rupted by a narrow inlet, and 
this in turn to an unbroken bay 
bar. Within a bay converging 
currents may build two spits toward each other until they 
form a bar (Figs. 59 and 60). As a rule the sea tends to build 
bars which are slightly concave toward the open water; or 
to drive back the central part of a bar more than the terminal 
portions until such concavity results. But where an embank- 




Fig. 60. — Spits converging to form 
a bay bar on the Alaskan coast. 



YOUNG STAGE 



301 



ment grows across the mouth of a narrow bay, and longshore 
current action is very powerful, the resulting bar may be 
quite straight. 

There is, however, an entirely different process by which bars, 
indistinguishable in surface form from those developed from 
growing spits, may be produced. Waves entering shallowing 
water may break before reaching the coast, and cast up the 
bottom debris into a narrow ridge, in the manner discussed 
more fully in connection with " Offshore Bars." The irregular 
bottom of a typical young shoreline of submergence is usually 
highly unfavorable to this process; but whenever the initial 
form or later deposition does give a fairly uniform slope to the 




Fig. 61. — Bay-mouth bars on the Marthas Vineyard coast. 



bottom near the shore, wave action may produce a bar inde- 
pendently of longshore transportation. Such a bar may form a 
short distance offshore and be driven in until the portion oppo- 
site a headland becomes a headland beach, and the portion 
opposite the bay remains a typical bay bar extending from 
headland to headland and nearly or quite closing the bay mouth ; 
or the waves may construct the bar just at the mouth of the 
bay in the first place; or they may break on the gently sloping 
bottom well within the bay and produce a bar near the middle 
or even near the head of the bay. It is possible that some 
supposed sandspits are really the beginnings of, or last rem- 
nants of, bars formed in this manner. 

A compound shoreline, like that of northern New Jersey, is 



302 



DEVELOPMENT OF THE SHORELINE 



especially apt to have an offshore bar pushed landward against 
projecting headlands, after which it will appear as a series of 
shorter bay bars. The bar across the mouths of the Shrews- 
bury and Navesink Rivers (Fig. 57) may have had an earlier 
existence as an offshore bar farther out in the Atlantic; but its 
history is not altogether simple, for it has been temporarily 
breached, and later rebuilt in part at least by longshore currents. 
The same is true of the bay bars closing Shark River and 
Manasquan River, which probably originated as parts of one 
offshore bar; while Metedeconk River will in the future be 

closed by the northern part of 
the offshore bar on which the 
town of Mantoloking is situated. 
It does not seem desirable to 
give separate names to bay bars 
formed in the two ways above 
described, because of the fact 
that the method of origin is 
often obscure. There are cases, 
of course, in which the process 
of formation may be inferred 
with reasonable assurance from 
the form or position of the bar; 
as for example when successive 
recurved points on the inner 
side of a bar indicate its development from a compound recurved 
spit, or the abutting of the bar at right angles against the shores 
of the bay show the predominant action of waves breaking on 
a shelving bottom. It is probably true, however, that in a 
majority of the cases where offshore wave action originates a 
bay bar, longshore transportation plays an important part in 
its further development. To determine the relative importance 
of the two co-operating forces may well be impossible. We 
will therefore name bay bars according to their position in the 
bays across which they have been extended, admitting the ex- 
istence of two processes which may independently or in co- 
operation produce them. On this basis we may recognize (1) 
bay-mouth bars (Fig. 50, bmb) or those extending from headland 
to headland across the mouths of bays, excellent examples of 
which are found along the shores of Marthas Vineyard Island 




Fig. 62. — Bay-mouth bar on the 
Marthas Vineyard coast. 



YOUNG STAGE 



303 



(Figs. 61 and 62) ; (2) bay-head bars (bhb) or those built a short 
distance out from the shore at the heads of bays, like the outer 
bar near Duluth at the head of the westernmost bay of Lake 
Superior (Fig. 63); and (3) mid-bay bars (mb) or those built 
across a bay at some point between its mouth and its head, a 




Fig. 63. — Bay-head bar near Duluth. 



good example being the bar which extends nearly across the 
middle of Hempstead Harbor, Long Island (Fig. 64). 

A headland which is bordered on either side by bay bars 
or spits is sometimes called a winged headland (" winged be- 
headland " of Gulliver 12 ). Grassy Hollow headland near the 
eastern end of Long Island is a typical specimen of this interest- 
ing form (Fig. 65). At Long Branch on the New Jersey coast 
we have the very large winged headland which Gulliver selected 
as his type example. 

After a bay bar has been constructed, the pond or lagoon 
enclosed behind it may gradually be transformed into a land 
area through the combined operation of several agencies. 
Streams from the land bring down sediment which may either 
be distributed over the floor of the lagoon by current action, 
or built into a bay delta which advances seaward until it meets 



304 



DEVELOPMENT OF THE SHORELINE 



the bar. Tidal currents carry debris, from the zone of wave 
agitation outside the bar, through the inlet, and distribute it 
over the lagoon bottom or build it into a tidal delta (Fig. 117) 
which projects into the lagoon with its surface usually below 



I 



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ypssopi^ 5 "^ 




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r 



hi 



■/* 



i^ik&fe 



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to h^|^;5& 

St 



■■ ~-"' -^-" •■■■•-' 



Fig. 64. — Mid-bay bar in Hempstead Harbor, Long Island. 



sealevel. Winds from the sea blow sand from the surface of 
the bar into the lagoon behind it, and may even cause sand 
dunes to migrate some distance into the enclosed area of quiet 
water. Large storm waves dash over the crest of the bar, 



YOUNG STAGE 



305 




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cr| 






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306 



DEVELOPMENT OF THE SHORELINE 



and their waters flowing down its landward side build wave 
deltas (Plate XLI) into the edge of the lagoon. Salt marsh veg- 
etation may secure a foothold in the areas of shallower water, 
and both by building up to the surface and by advancing over 




'^ 



.^ 






^szwm 




Fig. 65. — Winged headland near Sag Harbor, Long Island. 

other portions of the lagoon may materially hasten the conver- 
sion of the entire area into land. The process of conversion 
goes on at very unequal rates in different places; it is essentially 
independent of the progress of shore development on the outer 
coast; and it may even depend mainly on forces which are 
not directly connected with marine agencies. 

In the literature on shorelines one not infrequently encounters 
the curious idea that bay bars are the product of river deposi- 
tion. The material of the bar is supposed to have been carried 
out to the mouth of the bay and dropped where the brackish 
bay water meets the salt water of the sea. Von Richthofen 13 
seems thus to account for the bay bars of his " Liman type " 
of coast, the standard example of which is the northwest coast 
of the Black Sea near Odessa; and this theory is adopted by 
Hentzschel 14 and others in discussing the same and similar re- 
gions. How the coarse sand and even larger debris often com- 
posing the bar could be carried through the quiet waters of the 



YOUNG STAGE 307 

bay, and why such debris was not deposited in the form of a 
delta where the river enters the bay head are matters not satis- 
factorily explained. 

Offsets, Overlaps, and Stream Deflection. — Where a bar has 
almost closed a bay mouth, a narrow tidal inlet maintains 
connection with the open ocean, and permits tidal currents to 
pass in and out of the lagoon. Rivers emptying into the lagoon 
may increase the outflowing currents; and where there is no 
tide the opening maintained principally by the outflow of river 
water alone might better be called an, outlet, were it not that 
similarity of form and the desirability of uniformity in usage 
make it expedient to apply the single term " inlet" to all these 
features. 

From the method of bar development it follows that an inlet 
is normally found at that end of a bar toward which the long- 
shore current responsible for its growth is moving. It frequently 
happens, however, that storm waves break through a bar and 
establish an inlet at some other point, often at or near the point 
of attachment with the mainland cliff. Thereupon the original 
inlet may close, while the new one begins to migrate in the 
direction of the longshore current in consequence of the fact 
that deposition constantly occurs at the end of the bar on the 
up-current side of the inlet, necessitating an excess of erosion 
on the other side by the transverse currents which insist on 
keeping the inlet wide enough to permit their passage. In this 
manner the new inlet migrates until it reaches the position of 
the original inlet at the down-current end of the bar, when the 
process may be repeated. Sometimes the older inlet is closed 
before a new one is opened, and the bar exists for some time 
without any opening. Shaler 15 was of the opinion that new 
inlets were due to the bursting out of dammed-up land waters 
which had been held in restraint by an unbroken bar; but all 
the evidence available seems to show that even where tidal 
influence is unimportant, new openings are most frequently 
cut from the seaward side by the attack of storm waves. On 
the New Jersey coast inlets through the bars which obstruct the 
mouths of Manasquan, Shark, and other rivers or bays are con- 
stantly closing and opening, and migrate uniformly in the direc- 
tion of the dominant longshore current. 

The migrating of an inlet under the influence of a longshore 



308 



DEVELOPMENT OF THE SHORELINE 



current is commonly accompanied by the development of fea- 
tures which may permit one to determine the direction of the 
current from accurate maps or charts. In many cases the 
part of the bar on the up-current side of the inlet is a little 
farther seaward than the part below the inlet, in which case 
the shore is said to be offset (Fig. 66, a). It is possible to have 
offsets where there is no inlet, as shown at h in the same figure. 
Very frequently a bar which offsets its remaining portion at an 
inlet also overlaps it as shown at c; and where a stream enters 
the sea without passing through a bay, the 
shifting of the inlet at the stream mouth may 
cause a pronounced stream deflection (Fig. 66, d) . 
^The longshore current or currents responsible 
for these features move from the outer toward 
the inner segments of the shore, or in the direc- 
tion of stream deflection, as shown in the figure. 
Direct observation of shore currents is compli- 
cated by the fact that at the time of observa- 
tion less important currents in an opposite 
direction may chance to prevail; but accord- 
ing to Gulliver 16 , who first emphasized the im- 
portance of offset, overlap, and stream deflection 
as indicators of current movements, the direc- 
tion of the dominant current is reliably indicated 
when one or more of the three features just 
mentioned is present. 

There is reason to believe, however, that 
direct wave attack may force one segment of 
a bar back of a neighboring segment, thus 
giving an offset which is quite independent of 
the direction of longshore currents. It might well happen that 
the resulting offset would be exactly opposed to that which would 
have been produced by current action. This seems to be the 
case on the southern part of the New Jersey shoreline, where 
the dominant current, as shown by the direction of inlet migra- 
tion, is southward; yet successive offsets give a false indication 
of a northward moving current. 

Stone Reefs. — Under special conditions ordinary bay bars 
or offshore bars may undergo a peculiar process of lithification 
which changes them into stone reefs. According to Branner 17 , 




Fig. 66. 



YOUNG STAGE 309 

who has described the remarkable series of stone reefs border- 
ing the coast of Brazil for a distance of 1250 miles between 
Ceara and Porto Seguro, the only essential difference between 
these reefs and ordinary sand bars and spits lies in the indura- 
tion of the upper ten or twelve feet of the sand through the 
cementing action of calcium carbonate. It appears that in 
and about the lagoons or ponds back of the bars abundant 
aquatic and semi-aquatic plants live and die. " The fresh 
water is thus rendered acid by the presence of large quantities 
of carbon dioxide produced by organic decomposition. The 
acid water on the land side percolating through the embank- 
ment of sand at low tide attacks the calcareous matter (frag- 
ments of shells, etc.) in the sand and passes seaward with it in 
solution, but as it comes in contact with the dense sea water 
on its way through the sand, the lime carbonate in solution is 
deposited in the interstices between the sand grains. In time 
the interstices are completely filled, and the sand bank is hard- 
ened and so solidified that the water can no longer soak through 
it." In Branner's opinion the essential conditions are the fol- 
lowing : lagoons or ponds nearly or quite closed by bars or spits ; 
abundant vegetation in or about these water bodies; fragments 
of shells, crinoids, coral, or other calcareous material in the bar 
or spit; and a high density of the sea- water. Stone reefs are 
rare because the combination of all these features is rare. Lithi- 
fied beaches originally composed of sand and gravel and later 
cemented by calcium carbonate were early described by Beau- 
fort 18 from the coasts of Asia Minor and Greece; while Cold 19 
reports stone reefs from this same general region which sepa- 
rate lagoons from the open sea and which must be similar to 
those studied by Branner. 

Looped Bars. — ■ The islands of a young shoreline of submer- 
gence are attacked from all sides by the waves; but the most 
effective attack is delivered upon the seaward side, because 
both the swells and the largest storm waves come from the 
open sea, and because wave refraction concentrates the energy 
of both types of waves upon the seaward side of islands as well 
as upon projecting headlands. As in the case of headlands, part 
of the eroded debris is carried out to a permanent resting place 
in deep water, part is temporarily deposited in depressions of the 
irregular sea floor near the land, and part is built into various 



310 



DEVELOPMENT OF THE SHORELINE 



types of beaches and embankments. Among the latter there 
are, in addition to the spits and bay bars already described, two 
forms peculiar to eroded islands: looped bars and tombolos. 

Little beach material can accumulate at the base of the ex- 
posed cliff on the seaward side of the island. Sometimes spits 
extend out on either side of the main cliff, usually with their 
axes directed backward toward the land. More often, perhaps, 
the debris is driven backward along either side of the island 
until the quieter water to leeward is reached. Here embank- 
ments of several types may form. Spits may trail backward 
from either side, maintaining a separate existence; or their ends 




Sliapkei I. 

700 Ft. 



Fig. 67. — Looped bar on shore of Shapka Island, Alaska. (C. S. Chart, 

8881.) 



may unite to form a looped bar (Fig. 50, lb). Shapka Island, 
Alaska (Fig. 67), and Cup Butte 20 , Utah, furnish good examples of 
looped bars, the latter existing as an elevated shore feature on a 
former shoreline of Lake Bonneville. In other cases one or more 
embankments will be extended until the island is directly con- 
nected with the mainland. The extension of the embankment 
may take place wholly in the direction from the island toward 
the mainland (Fig. 68) ; or wholly from the mainland toward the 
island, especially in those cases where longshore currents build 
a spit out laterally until it forms a bar which connects with an 
island lying to one side of the cliffed headland; or the em- 
bankment may be constructed from both directions at the same 
time until the ends meet to form a connecting bar; or, finally., 



YOUNG STAGE 



311 



the bar may be built up simultaneously along its entire length 
by wave action on a shallowing bottom (Fig. 69). Furthermore, 
the mainland may be replaced in any of the above instances by 
another island, without altering the essential relations. In all 
of these cases the connecting bar is called a tombolo (Fig. 50, t). 

Tombolos. — The name " tombolo " was applied to the con- 
necting bar by Gulliver 21 in the following words: " Upon the 
coast of Italy where island-tying 
in its various stages is beautifully 
shown, such a bar is called a tom- 
bolo. For convenience in distin- 
guishing island-tying bars from 





Fig. 68. — Renard Island near Seward, 
Alaska, showing embankment grow- 
ing from island toward mainland. 



Fig. 69. — Inner Iliasik Island, 
Alaska, showing embankment 
which may be upbuilding to- 
ward the surface simultane- 
ously along its entire length. 



those of other kinds, the writer proposes to call every bar of this 
kind a tombolo, giving an English plural tombolos." Professors 
Olinto Marinelli of Florence and Giuseppe Ricchieri of Milan have 
both expressed to me orally their opinion that the term tombolo in 
the Italian language is restricted to the sand dunes found upon 
shore beaches and in other localities, and that it cannot properly 
be applied to a bar built by currents and waves. There seems 
to be no doubt that the plural " tomboli " does signify sand 



312 



DEVELOPMENT OF THE SHORELINE 



dunes or similar small mounds. On the other hand, it would 
appear that failure of the popular mind to appreciate the inde- 
pendent origin of the bars and the dunes which surmount 
them, had resulted in the application of the term tomboli to 
the bars themselves, at least in some parts of Italy. This fact, 




Fig. 70. — Single tombolo connecting former island of Marblehead with the 

mainland. 



and the confusion of ideas responsible for it, are both shown in 
the following quotation from Pianigiani's Dizionario Etimolo- 
gico della Lingua Italiana 22 : " ' Tomboli ' is a term com- 
monly applied figuratively to the mounds of sands which the 
sea forms in the fashion of banks on the shore; otherwise called 
' cotoni ' = ' costoni ' from ' costa: ' for example, ' the sea, 
roughened by opposing currents or winds, scrapes the bottom 
and brings the sand back to the shore, forming tumoli or tomboli, 
and makes bars or shoals at the mouth of the Arno. These 
tomboli are the same thing as the famous dunes of the Dutch 



YOUNG STAGE 



313 



and French' (Targioni, Viaggi)"* Prof. A. A. Livingston of 
Columbia University, to whom I am indebted for calling my 
attention to the foregoing citation, informs me that small mounds 




Fig. 71. — Former island of Big Nahant tied to Little Nahant, and the 
latter to the mainland by single tombolo. 



in the lagoon at Venice, which are visible only at low water, 
are called " tomboli " in the Venetian dialect; and Prof. F. C. 
Ewart of Colgate University states that Petrocchi gives as one 

*' " ' Tomboli ' si chiamano comunemente per similitudine que' monti- 
celli di rena, che il mare forma a guisa d'argini sulla spiaggia, altrimenti 
Cotani = Costoni da Costa: per es, "' il mare tempestoso per traversia rade il 
fondo e riporta al lido quella rena, e forma i. tumoli o i tomboli, e fa de* 
ridossi o interramenti alia bocca d'Arno. Essi tomboli sono la medesima cosa 
che le famose Dune degli Olandesi e Franzesi'. (Targioni, Viaggi.) " 



314 



DEVELOPMENT OF THE SHORELINE 




2 



YOUNG STAGE 315 

meaning of the word: " a small bank of sand thrown up by the 
sea." On maps of the Institute Geografico Militare of Italy 
such names as " Tombolo della Giannella " and " Tombolo di 
Feniglia " are printed along bars connecting islands with the 
mainland. The fact that the singular form " tombolo " is used, 
rather than the plural " tomboli " suggests that the term refers 
to the bar itself, and not to the series of dunes which may occur 
upon it. 

For the reasons outlined above, and for the further reason 
that the term tombolo has been introduced into a number of 
English discussions of shorelines, and even into some reports 
published in foreign languages, it seems advisable to adopt 
Gulliver's usage, rather than to use the double term " connect- 
ing bar " (which might equally well apply to a bay bar connect- 
ing two headlands), or to invent a new term. A single short 
term is desirable for the form under discussion, and notwith- 
standing the lack of uniformity and precision in the Italian 
use of the term " tombolo," its adoption into the English lan- 
guage with the restricted meaning given to it by Gulliver best 
meets the needs of the case. 

If the former island is connected with the mainland or with 
another island by a single, simple bar, we have a single tombolo 
(Fig. 70 and Plate XLII) . On the Massachusetts coast Big Nahant 
is tied to Little Nahant, and Little Nahant to the mainland by 
single tombolos in the construction of which onshore wave action 
on a shallowing bottom has probably played an important part 
(Fig. 71). A beautiful example of closely similar form is fur- 
nished by Duxbury Beach and Saquish Neck near Plymouth 
Harbor on the same coast (Fig. 72). Islands close to the main- 
land, or of comparatively large extent alongshore, may be 
connected with the mainland by a double tombolo or even a 
triple tombolo. Monte Argentario (Fig. 73) is tied to the west 
coast of Italy by a double tombolo, and a third uncompleted 
bar shows that the connection just escaped being a triple tom- 
bolo. Where two embankments extending backward from an 
island or outward from the mainland unite to form a single 
ridge before the connection is completed, we have a Y-tombolo, 
the type example of which is Morro del Puerto Santo (Fig. 74) 
on the Venezuelan coast 23 . Complex tombolos result when sev- 
eral islands are united with each other and with the mainland 



3 km 




Gurnet Pt. 



Saquish Head 



Fig. 72. — Duxbury and Saquish Neck tombolos uniting former islands with 
the mainland of Massachusetts near Plymouth. 

Page 316 



YOUNG STAGE 



317 




Fig. 73. — Monte Argentario, Italy, tied to the mainland by a double 

tombolo. 




318 DEVELOPMENT OF THE SHORELINE 

by a complicated series of bars. Nantasket Beach (Figs. 75 and 
76) on the Massachusetts coast is an excellent example of this 
form, in which the prograding of some of the bars has produced 
a series of beach ridges extending over a breadth of half a mile. 
The complicated history of this remarkable tombolo has been 
fully discussed by Johnson and Reed 24 . It should be noted that 

the term tombolo refers to the con- 
necting bar itself, and not to the former 
island as has been assumed by several, 
including Hobbs 25 , who employs the 
spelling " tombola " and assigns to it 
a Spanish origin. This last was pre- 
sumably due to an oversight, as I can- 
not find authority for a Spanish form 
of the word. 

Fig. 74. — Morro del Puerto Cuspate Bars. — It occasionally hap- 

Santo, Venezuela, a Y- ,, , ., -, . -, ■, -. , 

, , \ pens that a spit which has advanced 

some distance into open water, re- 
curves (Fig. 77) until it again unites with the shore at its distal 
end, thus producing a bar which is more or less cuspate according 
as the seaward angle is fairly sharp or broadly rounded. An unu- 
sually sharp angle may result if a secondary spit trails abruptly 
back toward the shore from the point of a primary spit. In other 
cases two spits may grow out from the shore toward each other, 
and finally unite to form a bar of sharply cuspate form. This 
often happens on the leeward side of an island, when it represents 
the early stage of a Y-tombolo. Sometimes the presence of a 
shallow some distance out from the main shore will cause the 
development of a bar of similar form whose apex is at the shal- 
low. Essentially identical in shape and origin is the bar which 
results when an island connected with the mainland by a double 
tombolo is consumed by the waves, leaving a V-shaped bar 
with the point of the V near the site of the former island. In 
both of the last two cases it is the obstruction in front of the 
main shore which determines the form and location of the 
resulting bar. 

Certain features are common to bars developed in the manner 
above described. All of them are more or less cuspate in form; 
all enclose a lagoon or swampy area; and probably all have 
been produced by the combined action of waves and currents. 



YOUNG STAGE 319 

It is frequently impossible to determine the precise manner in 
which a given bar originated and developed. For this reason 
it seems wisest, as in the case of bay bars, to group the similar 
forms under a single name, recognizing the fact that different 
examples may have originated in different ways. The name 
V-bar has been applied to some of these forms; but because of 
their relation to cuspate forelands, described below, we will 
employ the term cuspate bar (Fig. 50, cb). 

Were the compound spit (Fig. 55) which protects Toronto 
Harbor to unite with the shore at its distal end, as Fleming 26 
considered a future possibility, we would have a compound cus- 
pate bar. Caseys Point (Fig. 78) and Gaspee Point (Fig. 79), 
Rhode Island, representing what Gulliver 27 calls the V-bar stage 
and lagoon-marsh stage of cuspate forelands, are good examples 
of simple cuspate bars which were probably developed from spits 
growing seaward toward each other, or from primary spits 
growing seaward and secondary spits extending from their distal 
points backward to the shore. At the southern end of Revere 
Beach near Boston is a cuspate bar produced by the removal 
of an island which was connected with the mainland by a double 
tombolo (Fig. 80). The shores of Port Discovery on the Wash- 
ington coast exhibit a beautiful series of cuspate bars in all stages 
of formation (Fig. 81). 

Cuspate Forelands. — In none of the shore forms thus far 
considered has there been any extensive forward building of 
the main shore into the water. Beaches, spits, bay bars, tom- 
bolos, and cuspate bars are either comparatively narrow, or, 
as in the case of some broad spits and tombolos, are connected 
with the land by narrow embankments. We must now con- 
sider a group of forms in which the shoreline is systematically 
prograded by wave and current action, and an appreciable 
area of more or less continuous dry land added to that pre- 
viously existing. The new land is sometimes called a beach 
plain; or, following Gilbert, a wave-built terrace. The latter 
term is more appropriate for the examples found on the elevated 
shorelines studied by Gilbert than for those on modern shores 
where the terrace effect is not evident because the top surface 
alone appears above water. We will follow Gulliver's sugges- 
tive terminology and speak of these features as forelands. They 
may have a variety of forms, but where most typically developed 



320 



DEVELOPMENT OF THE SHORELINE 







o,BI 



^ 




SSfcj 



- X LHI 



sk ...... 






■■:-:\\M 



'•V-,BL 



Mi-A-. SL 



::-.WL 




Fig. 75. — Former islands, many of which were wholly or completely eroded 
by wave action, and the resulting debris used by the waves to build a 
complex tombolo tying the remaining islands to the mainland. Dotted 
contours show islands wholly destroyed, broken contours the eroded 
portions of islands but partially destroyed. (Johnson and Reed.) 



YOUNG STAGE 



321 




Fig. 76. — Nantasket Beach, Massachusetts, the complex tombolo formed 
by wave erosion of the islands shown in Fig. 75, with deposition of the 
debris to give connecting beaches uniting the remaining islands with 
each other and with the mainland at the south. (Johnson and Reed.) 




Fig. 77. — A strongly recurved spit on 
the Washington coast, about to 
become a cuspate bar. 




Fig. 79. — Cuspate bar showing 
enclosed marsh near Provi- 
dence, Rhode Island. 




BOUlderS (remains of 

...■..".'• Cherry Island) 



Fig. 80. — Cuspate bar originally built as a 
tombolo tying to the mainland an island 
since removed by wave erosion. 
Page 322 



rreenesPt 



: $fc- 



Plum 
►each 






,!\* 






Caseys Pt. 



Fig. 78. — Cuspate bars on the 
Narragansett Bay shore. 




Page 323 



324 



DEVELOPMENT OF THE SHORELINE 



are more or less triangular in shape with the apex of the triangle 
pointing out into the water (Fig. 82); they are then called cus- 
pate forelands 28 . A change in 
the outline of the shore or in 
the configuration of the sea- 
bottom often occasions their 
development, while in other 
cases no assignable cause is 
apparent. 

There is no sharp dividing 
line between a compound 
cuspate bar in which the 
successive embankments are 
closely spaced, and a cuspate 
foreland in which the differ- 
ent beach ridges are widely 
enough separated to enclose 
strips of lagoon or marsh. Transition forms between the two types 




Fig. 82. — Cuspate foreland near Port 
Townsend, Washington. 




Fig. 83. — Types of cuspate foreland bars. 



exist, and might appropriately be termed cuspate foreland bars 
(Fig. 83, a). Another intermediate form, properly classed under 



YOUNG STAGE 325 

the same term, is produced when a typical cuspate bar enclosing 
a triangular lagoon or marsh (Fig. 83, b) is prograded by the addi- 
tion of successive beach ridges upon its seaward side. If the 
lagoon or marsh strips are a minor feature, or if the initial tri- 
angular lagoon is very small as compared with the total surface of 
added land, then the forms are called simply cuspate forelands. 

I have found it profitable to recognize three principal types 
of cuspate forelands. When the shore is aggraded on both 
sides, so that fairly symmetrical lines of growth (beach ridges 
and swales) run parallel with both shores of the cusp, we have a 
simple cuspate foreland. In one of its former positions Cape 
Canaveral seems to have been a fairly good example of this 
type (Fig. 84). Where erosion attacks one side of the cusp 
to such an extent that no ridges and swales remain parallel to 
that shore, but the shoreline obliquely truncates these lines of 
growth, a truncated cuspate foreland is produced. As the type 
example of this form we might cite the Darss foreland on the 
Baltic coast of Germany (Fig. 131), whose western shore abruptly 
truncates a magnificent series of ridges and swales. Occasion- 
ally a truncated cusp of this type is later prograded, giving 
ridges and swales parallel to the new shoreline; and the proc- 
ess of alternate retrograding and prograding may be repeated 
a number of times with constantly varying direction. The 
resulting forms will be designated as complex cuspate forelands. 
To this class belongs the present Cape Canaveral, on which 
several distinct series of ridges and swales have been successively 
truncated (Fig. 129). The Dungeness (Fig. 130) of southeastern 
England is moderately complex near its seaward point. 

It should be noted that Cape Canaveral occurs on a shoreline 
of emergence. It is cited here because cuspate forelands occur 
on all classes of shores, and because it affords unusually good 
examples of two of the three types of cuspate forelands defined 
above. 

* Marsh Bars. - — An interesting form, not generally recognized, 
is produced by marine erosion of the seaward edge of a marsh 
which was originally unprotected from the sea by any barrier 
of sand or gravel. Wave attack separates the vegetable matter 
of the marsh from the sand which is usually present in greater 
or less amount, and casts the sand upon the edge of the re- 
maining marsh in the form of a narrow ridge. On the map such 




Page 32G 



YOUNG STAGE 



327 



a ridge will look like a narrow offshore bar with a later formed 
marsh back of it. In reality the marsh is the older, and the 
ridge is quite unlike an offshore bar in origin. The smaller 
size, lack of continuity, and the irregular pattern of these marsh 
bars will generally distinguish them from true offshore bars. 
They are usually found bordering unexposed shores where un- 
protected marsh deposits could persist for a long time, suffer- 
ing only gradual removal by small sized waves. Along the 




Fig. 85. — Marsh bars on the Delaware Bay shore. 

Delaware Bay shores of New Jersey marsh bars are numerous, 
Robinson's Beach near the mouth of Dennis Creek being a good 
example (Fig. 85). The fact that some foreign debris may be 
brought to such a bar by waves and currents is immaterial, the 
essential point being that the marsh is older than the bar, and 
has never been bordered by a true offshore bar formed by wave 
action on the sea-bottom. 

Flying Bars. — After a spit or looped bar has grown backward 
from an island, it sometimes happens that the island itself is 
entirely removed by wave attack before the spit or bar is de- 



328 DEVELOPMENT OF THE SHORELINE 

stroyed. We then have a flying bar, isolated in the open water. 
Gulliver 29 , who originated the term, suggested that Sable Island, 
an isolated bar of unconsolidated sand off the coast of Nova 
Scotia, may be a flying bar left in its exposed position by the 
consumption of a former island to which it was attached. 

Bay Deltas. — Streams entering the heads of drowned valleys 
will deposit sediment to form deltas, providing their currents 
transport more debris or debris of larger size than the marine cur- 
rents in the bay can remove. The deltas normally advance from 
the heads of the bays toward the bay mouths, and may be des- 
ignated by the term bay deltas (Fig. 50, bd). They often extin- 
guish the lagoons left back of bay bars, or completely fill open 
bays, thus assisting the shore processes in their efforts to sim- 
plify the shoreline. It should be remembered, however, that 
they are the products of normal stream action, and are deposited 
in spite of marine processes, rather than because of them. For 
this reason it is a mistake to treat them as one of the forms 
resulting from the normal tendency of marine forces to simplify 
ragged coast. We must rather regard them as extraneous 
features whose effect in straightening the shoreline is wholly 
incidental and accidental, and quite independent of the processes 
by which waves and currents work toward the same result. 

Stages of Development of Shore Details. — It may have 
been observed that in the preceding discussions of beaches, spits, 
bars, tombolos, forelands, and deltas, no account has been taken 
of successive stages of development of these forms. They have 
been described as forms especially characteristic of a young 
shoreline of submergence, but young, mature, and old stages 
of recurved spits, bay bars, and all the other forms mentioned, 
have not been recognized. The omission was intentional, and 
is due to the writer's doubt of the wisdom of attempting to clas- 
sify the details of shore forms into definite stages of development. 
Inasmuch as this doubt has not been shared by all students of 
shoreline physiography, it is desirable that the grounds for its 
existence be made plain. 

The greatest value of recognizing sequential stages of land- 
form evolution is the aid thus given to a clear comprehension 
of the shape and significance of the forms in question. Assuredly, 
the introduction of the evolutionary idea into the study of 
river valleys, coastal plains, mountains, and other major land- 



STAGES OF DEVELOPMENT OF SHORE DETAILS 329 

forms has shed a flood of light upon their present shapes and 
their past and future histories. We have seen that the shore 
profile cannot be fully understood except in the light of its 
successive and orderly stages of development; and the same is 
true of the outline of the shore as a whole. On the other hand, 
it may well be doubted whether it is profitable to push the 
developmental idea so far as to apply it in the explanation of 
all the detailed forms which are merely incidents in the evolu- 
tionary history of some major topographic unit. The term 
" young river " is full of significance for the student of land- 
forms; but I doubt whether anyone will profit from an attempt 
to recognize young, mature, and old stages of sandbars, which 
may occur in any or all of the different stages of river develop- 
ment. Similarly, I find unlimited value in the recognition of 
young, mature, and old stages of shorelines; but am not con- 
vinced that there is profit in the effort to classify all the details 
of a young shoreline, for example, into three or more special 
stages of development. Unless it shall appear that the under- 
standing of shore forms is materially aided by such attempted 
classification, we may better restrict the application of terms 
indicative of developmental stages to the shoreline as a whole, 
rather than extend their use to each of its many parts. 

A further reason for not recognizing definite successive stages 
in the development of spits, bars, forelands, etc., is the difficulty 
of determining any regular and orderly succession of features 
which will be common to all forms of a given class, and which 
are genetically related to true shoreline processes. The best 
attempt to classify shore details into stages of development is 
that made by Gulliver; but the results of that attempt are 
not altogether satisfactory. Thus the youth of a tombolo is 
assumed to be represented by one or two cuspate forelands 
projecting from mainland toward island, or island toward main- 
land, or both, even though the intervening channel may be so 
deep that further growth of the forelands is impossible. 30 On 
this basis, a tombolo which had been entirely completed, and then 
broken through by storm waves, would be called " young." 
A completed tombolo is said to be in " adolescence," or, if the 
island happens to be nearly or quite eroded away, " late adoles- 
cence;" while "the mature stage of island-tying is where the 
islands and their connecting tombolos are completely consumed 




Fig. 47. 




Fia. 50. 



STAGES OF DEVELOPMENT OF SHORE DETAILS 331 




Comparison of text figures to facilitate correlation of successive stages in 
the development of a shoreline of submsrgence. 

Fig. 45. — Initial stage. 
Fig. 47. — Early youth. 
Fig. 50. — Youth. 
Fig. 87. — Submaturity. 
Fig. 88. — Maturity. 
bd, bay delta; bh, bayhead beach; bhb, bayhead bar; bmb, baymouth bar; 
bs, bayside beach; cb, cuspate bar; cf, cuspate foreland; ch, cliff ed 
headland; crs, compound recurved spit; cs, complex spit; hb, headland 
beach; lb, looped bar; mb, midbay bar; rs, recurved spit; s, spit; t, 
tombolo; wh, winged headland. 



332 DEVELOPMENT OF THE SHORELINE 

by the sea 31 ." Surely the developmental idea is forced beyond 
the limits of its usefulness when the complete annihilation of a 
given form is called its " maturity." One reason for the unsatis- 
factory character of this classification is that it represents an 
attempt to harmonize the stages of tombolo formation with the 
stages of shoreline development, an attempt which must always 
end in failure for the reason that the isolated, detailed forms of 
an irregular shoreline, even if they develop systematically, cannot 
develop synchronously with the shoreline as a whole. Tombolos 
may be made and destroyed while the shoreline is still in its 
youth. 

Gulliver's attempt to classify bay bars according to stages of 
development is equally unsatisfactory. The basis of classifi- 
cation was made the extent to which the bay was filled by a 
stream delta or other deposits. Since these deposits are quite 
independent of the bar itself, and are found abundantly in bays 
which have no bars, they can scarcely be accepted as a proper 
basis for the classification of bars into young, adolescent, and 
mature examples. If bay bars have any orderly sequence of 
forms characteristic of different stages of their development, 
they must be classified, if at all, on the basis of those forms, and 
not on the relative size of wholly extraneous features, such as 
river deltas, which may happen to lie back of them. 

In discussing cuspate forelands Gulliver drops the terms youth, 
adolescence, and maturity, for reasons which are not clear, and 
speaks of " three stages of progressive development, — the V-bar 
stage, the lagoon-marsh stage, and the filled stage." He recog- 
nizes that the first two stages are not represented in the history 
of those forelands which build out continuously from the 
mainland. Bay deltas are classified as young, adolescent, or 
mature according to the extent to which they fill the bay into 
which they happen to be built. Of three deltas identical in size, 
shape, and composition, but built into three bays of increas- 
ing length measured from head to mouth, one would be called 
mature, another adolescent, and the third young. Ordinary 
deltas are classified, not according to stages of development, 
but according to form as determined by the ratio of activity 
between river and marine currents, because it was not found 
practicable to discover laws of progressive delta development 
when the deltas did not occur in bays. This fact must lead us 



DIFFERENT MARINE FORCES 333 

to question the value of classifying into definite stages of devel- 
opment those deltas which happen to be located in bays; espe- 
cially when such classification is based, not upon real differences 
in the characteristics of bay deltas at different periods of their 
formation, but upon the non-significant ratio of delta size to size 
of bay. Gulliver makes no attempt to divide spits into stages 
of development 32 . 

Enough has been said to show the difficulty of classifying the 
details of shore forms into progressive stages of systematic 
development. It is clear that, at least in the present state of 
our knowledge, such classification is neither profitable nor feasible. 
This conclusion is perfectly compatible with the belief that 
shore profiles and shore outlines pass through perfectly definite 
stages of development, the proper recognition of which is essen- 
tial to a full understanding of shore forms. Gulliver rendered a 
valuable service to physiography by applying the principles of 
landform evolution to the study of shorelines on a scale never 
before attempted. That he may possibly have carried the 
attempt too far does not affect the fundamental importance of 
his thesis. 

Relative Importance of Different Marine Forces in the Forma- 
tion of Bars, Forelands, Etc. — throughout the discussions of 
beaches, spits, bars, tombolos, and forelands which have occu- 
pied our attention on preceding pages, no special consideration 
was given to the marine forces which produced those forms. 
It was stated that waves or currents operated in certain ways, 
but ordinarily neither the methods of wave action nor the 
kinds of currents were discussed. In previous chapters we have 
analyzed the behavior of waves and currents of different types 
at some length; but it remains to answer the important ques- 
tion as to which of these agencies are primarily responsible for 
the detailed forms found on a young shoreline of submergence. 

Gulliver 33 recognizes three marine agents: waves, tides, and 
currents. A careful reading of his essay on " Shoreline To- 
pography " shows that under " waves " he does not clearly 
recognize the highly important wave currents, but only the 
destructive effects of wave impact; by " tides " he means tidal 
currents; and under " currents " he refers to planetary currents 
and local wind currents. He is " inclined to attribute the attack 
of the sea largely to the waves, and its transporting action largely 



334 DEVELOPMENT OF THE SHORELINE 

to the tides and currents; " and throughout the discussion of 
individual shore forms he adheres to this idea of transporta- 
tion largely by tidal, planetary, and wind currents. There are, 
it is true, isolated statements which taken alone seem to indi- 
cate a fuller recognition of wave-current action; but the treat- 
ment as a whole practically excludes this important process. 
Thus in discussing the origin of cuspate forelands in estuaries 
Gulliver shows that planetary currents cannot operate in such 
localities, and that wind currents are so weak as to be over- 
powered by the tides; he therefore concludes that tidal cur- 
rents must be responsible for the forms in question. Wave 
currents and the associated "beach drifting" are not even re- 
ferred to in this connection. The failure to recognize the 
very great efficiency of wave currents in moving shore debris is 
responsible for the idea, repeatedly expressed in Gulliver's 
essay 34 , that important longshore transportation does not take 
place until more waste is supplied to the sea than can be de- 
posited offshore. This might be true if, as Gulliver supposed, 
shore debris were dependent upon tidal, planetary, and wind 
currents for its transport; for not until the irregularities of 
sea-bottom and shore outline have been measurably smoothed 
out by local deposition, or the shore has reached its " adoles- 
cent stage " according to Gulliver, can these larger currents 
sweep uninterruptedly along the coast. Wave currents, how- 
ever, will operate effectively on any shore which is fronted by 
a body of water sufficiently large for the generation of waves; 
and the most irregular shore will, even in its youthful stage, 
experience a very considerable amount of longshore beach 
drifting. 

There can be no doubt that wave currents and the associated 
longshore beach drifting play a very important role in the 
formation of various types of beaches, spits, bars, tombolos, 
and forelands. Tarr 35 has shown that cuspate forelands, bay 
bars, tombolos, and spits are built by wave action in lakes and 
nearly tideless bays where tidal and other currents are either 
wholly inoperative or far too weak to move the material with 
which the forms have been constructed. Woodman 36 has pre- 
sented convincing evidence that in the Bras d'Or Lakes of Cape 
Breton Island cuspate forelands, tombolos, bay bars, loop bars, 
and spits are formed by wave action without material aid from 



DIFFERENT MARINE FORCES 335 

tidal, wind, or other currents. Wilson's studies 37 , on the shore 
forms of Lakes Erie and Ontario, and the Bay of Quinte lead to 
a similar conclusion. The tideless shores of the island of Rugen 
in the Baltic, as described by Philippson 38 , exhibit numerous 
spits and bay bars composed of material transported almost ex- 
clusively by wave currents. A small cuspate foreland on the 
shore of Lake George is described by Comstock 39 , as having 
been formed through the action of waves generated by passing 
steamboats. 

Even where tidal and other currents not related to wave action 
move with high velocity in the offshore zone, the waters near 
the shore, where the forms in question are built, commonly 
have a movement too feeble to transport the gravel and cobble- 
stones of which many forelands and embankments are composed. 
On the other hand, wave currents near the shore are exceedingly 
powerful, and may easily be observed to drive the coarsest 
debris along the coast with a rapidity which is sometimes sur- 
prising. Wheeler 40 repeatedly observed half bricks on a shingle 
beach carried 25 to 30 yards in from l\ to 2 hours, and quotes 
de Ranee as authority for the drifting of encaustic tiles by a 
gale for a distance of "1 mile in two tides." Shaler reports 
the movement of pieces of brick by oblique wave action at the 
rate of more than half a mile per day. Wind currents in the 
shallow waters near the shore, and hydraulic currents generated 
by the combined action of waves and wind, while generally too 
feeble to move coarse debris without the aid of wave currents, 
frequently co-operate in a most effective manner with wave 
currents in causing a comparatively rapid and exceedingly im- 
portant longshore transportation of both fine and coarse mate- 
rial. It is often feasible to demonstrate that the material of a 
given foreland or embankment is derived from a neighboring 
cliff, that beach drifting from the cliff toward the area of accumula- 
tion proceeds actively under the influence of waves, and that no 
other type of currents are known to exist which are of sufficient 
velocity to move the debris undergoing transport. It would 
seem logical to conclude that wave currents are mainly respon- 
sible for the production of the forms in question. 

It has sometimes been held that the waves merely agitate the 
debris near the shore and by repeatedly raising it from the 
bottom make it possible for even weak tidal currents to effect a 



336 DEVELOPMENT OF THE SHORELINE 

longshore transportation of coarse material. There can be no 
doubt that tidal and other currents often co-operate with wave 
currents to effect the distribution of shore debris; but it should 
be remembered that wave currents are ^independently capable 
of moving the coarsest material along the shore for indefinite 
distances. Gravel and cobblestones would be carried along a 
coast by wave currents and built into various types of forelands 
and embankments, even were there no assistance from tidal and 
other currents; but these latter currents would in general be 
powerless to move such coarse debris in the immediate vicinity 
of the shore unless aided by waves; a fact fully appreciated 
by Gilbert 41 . I find it impossible, however, to accept Gilbert's 
further conclusions that " the transporting effect of waves alone 
is so slight that only a gentle current in the opposite direction 
is necessary to counteract it," and " the concurrence of waves 
and currents is so general a phenomenon, and the ability of 
waves alone is so small, that the latter may be disregarded 42 ." 
*" One must, however, fully recognize the possibility that tidal 
and other currents may be primarily responsible for the location 
and development of some forelands and embankments. For 
the production of these forms it is only necessary that shore 
debris shall be transported to a certain locality and there de- 
posited. It is immaterial what type of current accomplishes 
the transportation. If tidal currents, or eddy currents, or cur- 
rents of any other type have the proper direction and strength 
to accomplish the observed results, their possible importance 
must not be overlooked simply because wave currents are known 
to have produced similar results elsewhere. The possibility that 
certain sandy cuspate forelands, spits, etc., are primarily the 
product of currents unrelated to wave action should especially 
be kept in mind. It may be difficult, or even impossible, to 
determine the relative importance of wave currents and other 
currents in such cases; but if the determination is at all possible, 
it can safely be made only by one who studies the individual 
examples in the field with an open mind, and who is fully con- 
vinced of the ability of wave currents, as well as other more 
generally recognized currents, to produce such forms. Abbe 43 
reports a case in which an eddy current generated by the ebbing 
tide seemed to him to be responsible for the development of a 
cusp on the sandy shores of Sassafras River in Maryland. As 



DIFFERENT MARINE FORCES 



337 



regards my own studies, I can say that I have found many 
forelands and embankments which seemed to me demonstrably 
due, principally if not wholly, to wave currents; but none which 
seemed undoubtedly the product of other types of currents. I 
am therefore inclined to believe that wave currents have played 
the most important part in the construction of all the sandy 
forelands and embankments of our coasts. 

Davis 44 refers briefly to an interesting cuspate bar on the 
south shore of Lake Balaton in Austria-Hungary, the posi- 







Fig. 86. — Lake Balaton (Platten Lake) showing position of cuspate bar. 



tion of which he regards as evidence that currents rather than 
waves control the development of such forms. On the basis 
of map study he concludes that a promontory which projects far 
into the lake from the north shore probably occasioned the 
development of two circling currents, and that in the quiet 
water between the two whirls, near the south shore, the cuspate 
bar was built. An outline map of the lake, showing the posi- 
tion of the bar, is represented in Figure 86. When due account 
is taken of the relation of fetch of open water to wave develop- 
ment, it will be seen that westerly winds must drive large waves 
eastward along the south shore of the western arm of the lake 



338 DEVELOPMENT OF THE SHORELINE 

as far as a point opposite the projecting promontory; but that 
beyond this point wave action from the west will be weakened 
because of the sheltering effect of the promontory and the re- 
sulting short stretch of open water across which west winds can 
blow. Northerly and northeasterly winds will drive fairly large 
waves against the south shore of the eastern arm of the lake, but 
just west of a point south of the promontory there will be a 
rapid decrease in the comparative effectiveness of waves from 
this direction. As a result of these conditions we should expect 
beach drifting along the south shore of the lake to be toward a 
point opposite the promontory for a considerable distance on 
either side of that point. It is not necessary, therefore, to 
assume the existence in Balaton Lake of two rotary currents 
of sufficient velocity near the shore to transport the debris 
which composes the cuspate bar, for a bar opposite the promon- 
tory is a perfectly normal and expectable result of wave action 
alone. It may even be shown that wind waves from a single 
direction are alone competent to build a cuspate bar at the 
point in question. 

The frequent appeal to a pair of hypothetical circling cur- 
rents or eddies with a triangular space of comparatively dead 
water between the shore and the point of tangency of the eddies, 
in order to explain the development of cuspate bars and fore- 
lands, has long seemed to the writer unnecessary, and insuffi- 
ciently justified by evidence of critical value. In many cases 
there is ample evidence that currents of some type effect the 
longshore movement of debris either toward or away from the 
point of the cusp; but in most cases the only basis for the sup- 
posed pair of circling currents is the assumption that they are 
required in order to explain the presence of a foreland of cuspate 
form. 

Both the development of cuspate bars and forelands, and the 
longshore movement of debris causing offsets, overlaps, and stream 
deflections, may usually be explained as the normal product of 
longshore beach drifting, assisted by the wind currents and 
hydraulic currents which ordinarily accompany that process. 
Thus the Darss foreland (Fig. 131) has been built with debris 
drifted eastward by the action of waves generated under west- 
erly winds, the beach drifting no doubt having been supple- 
mented by water forced eastward by the friction of the wind 



MATURE STAGE 339 

on the sea surface, and by eastward moving hydraulic currents 
which would attempt to remove the water piled against the 
coast by wind and waves. As the point of the Darss advanced 
northward it gradually sheltered the waters to the eastward from 
westerly winds, and gave the waves generated by easterly winds, 
formerly overpowered by the dominant action from the west, an 
opportunity to determine the movement of shore debris. Con- 
sequently beach drifting from east to west has apparently pre- 
vailed east of the northward projecting point of the Darss in 
recent times, and has doubtless caused the westward deflection 
of the Prerow River. In a similar manner the Carolina capes, 
regarded by Gulliver 45 and Davis 46 as having been built between 
pairs of circling currents, may be explained as the expectable 
result of normal wave action. In neither case, nor in any other 
known to the writer, does it seem necessary to assume the exist- 
ence of pairs of rotary currents, the evidence for which is either 
inconclusive or wholly lacking. 

Mature Stage. — We have inquired at some length into the 
series of forms which characterize the young shoreline of sub- 
mergence, and have found that the unorganized condition of 
current action along such a shore combines with the initial 
irregularities of the submerged land area to produce an almost 
endless variety of interesting shore features. In striking con- 
trast with the complexity and variety of youth is the simplicity 
of the mature shoreline of submergence (Fig. 88). Let us 
trace briefly the steps by which that simplicity is attained. 
During its initial stage a shoreline of submergence is wholly 
unadjusted to the waves and currents which operate upon it. 
Waves break irregularly upon the uneven bottom and against 
the complicated shoreline; currents are split up and deflected 
in every conceivable direction, and any branch current may 
find itself flowing swiftly against some headland or over some 
shallow at one moment, and dropping its load a moment later 
when its velocity is checked upon passing into deep water 
opposite some bay. This unadjusted condition continues in 
constantly diminishing degree throughout the youth of the 
shoreline of submergence and is characteristic of that stage of 
its development, just as an irregular longitudinal profile is char- 
acteristic of the young stage of stream development. But the 
removal of outlying islands, the cutting back of projecting 



340 



DEVELOPMENT OF THE SHORELINE 



headlands, and the building of bars across the mouths of bays, 
gradually simplify the outer shoreline and permit longshore 
currents to move through greater distances unimpeded by pro- 
jecting land masses. At the same time wave action has estab- 
lished the shore profile of equilibrium on the seaward side of the 
bars and is working toward the same end on the cliffed head- 
lands. Thus the shoreline progresses toward maturity. When 
the headlands are partially cut back and many of the interven- 
ing bays are nearly or quite closed by bars, so that longshore 
currents may move through considerable distances before en- 




Fig. 87. — Shoreline of submergence, submature stage. 



countering obstructions, the shoreline may be said to have 
reached late youth or submaturity (Fig. 87). 

Still later the headlands will be so far cut back and bay-mouth 
bars will be so uniformly present opposite the original re-entrant 
angles of the coast, that a very simply curved or nearly straight 
shoreline will permit longshore currents to transport debris for 
indefinite distances without hindrance. The shoreline is now 
nicely adjusted to the forces operating upon it; the beach 
profile of equilibrium is fully established both on the seaward 
side of the bars and at the bases of the retreating cliffs; and 
while the cliff profile may still be too steep to permit one to call 
the entire shore profile mature, the shore outline is such that 
debris moves with the longshore currents as systematically as 



MATURE STAGE 



341 



sediment is moved seaward on the nicely adjusted slope of a 
graded river. In short, the shoreline itself has reached a graded 
condition; and this condition has been attained by an orderly 
process of cutting back the headlands and bridging the bays 
with the resulting debris, just as the grading of the river is 
accomplished by cutting down projecting rock masses and fill- 
ing depressions with the erosion products. The establishment 
of the graded condition marks the entrance of either river or 
shoreline into the early mature stage of its development. 

Full maturity (Fig. 88) is attained only when the shoreline has 
been pushed inland beyond the bay heads, and lies against the 




Fig. 88. — Shoreline of submergence, mature stage. 

original mainland throughout all its course. By this time the 
numerous islands and prominent headlands of youth have been 
obliterated, the great variety of spits, bars, tombolos, and fore- 
lands have disappeared, bay deltas and marsh deposits have 
been consumed by the advancing waves, and there remains 
only a comparatively narrow beach at the base of an almost 
continuous marine cliff which borders a shoreline of very simple 
curvature. Monotony rather than variety is the distinguishing 
feature of maturity, although the cliffs, often covered with vege- 
tation, may be of such magnitude as to impart majestic grandeur 
to the coastal scenery. 

Even in the maturity of a shoreline of submergence the ad- 



342 



DEVELOPMENT OF THE SHORELINE 




§1 

•§* 

Is 



MATURE STAGE 



343 



vance of the waves may be so rapid that stream erosion cannot 
lower valley floors as fast as the shoreline is cut back. This is 
especially apt to be the case where streams are small and weak, 
and where the nature of the country rock permits much under- 
ground seepage and little surface erosion. Hanging valleys due 
to this cause are developed on a small scale along many coasts 
(Plate XLIII), but are especially striking on the mature coast 
of northwestern France (Plate XXI), where many valleys are 
left hanging in the face of the chalk cliffs because wave erosion 




Fig. 89. — Valleuses on the northwest coast of France. 



cuts the cliffs backward faster than the smaller streams can cut 
their valleys downward. These hanging valleys have been given 
a special name, " valleuses," by the French, and by their frequent 
convergence toward a point some distance out to sea (Fig. 89), 
they furnish an indication of the extensive wave erosion which 
has removed the main valley they once united to form. Only 
the larger streams have been able to reduce their gently sloping 
valley floors to sealevel as fast as the waves cut inland, and their 
valleys form the only interruptions in a line of cliff which extends 
for many miles in very simple curves. Where streams are un- 
able to reduce a whole broad valley as rapidly as the shoreline is 



344 DEVELOPMENT OF THE SHORELINE 

worn back, we may find a narrow gorge cut in the bottom of 
the broad valley, the bottom of the gorge alone being reduced to 
an accordant junction with the sea. 

Not all parts of a shoreline develop at the same rate. Along 
weak rock coasts maturity is attained more quickly than along 
coasts composed of more resistant material. Even after matur- 
ity is attained the shoreline on a broad belt of weak rocks will 
retreat more rapidly than adjacent sections, until the depth of 
the indentation has so weakened wave attack that a condition 
of equilibrium is attained. Thereafter all parts of the shore- 
line retreat at the same rate, the portion bordering the weak 
rock area keeping a constant distance in advance (farther in- 
land). The initial more rapid retrogression of the shoreline 
on weak rocks depends primarily on two factors: in the first 
place the weak rocks yield more readily to wave attack; and in 
the second place, weak rock areas are normally worn down nearer 
to sealevel by subaerial agencies, with the result that waves 
and currents have to dispose of much less debris than they do 
where high cliffs shed vast quantities of waste upon a slowly 
retrograding beach. A mature coast should therefore show 
simple but distinct curves systematically related to rock struc- 
ture. 

Exposed shorelines develop more rapidly than do protected 
shorelines, a fact well illustrated by the more advanced stage of 
development reached on the Atlantic coast of the Maryland- 
Delaware coastal plain, as compared with the Chesapeake Bay 
coast of the same district. Other factors likewise retard or 
accelerate shoreline development, with the net result that a 
shoreline approaching maturity may consist of a series of more 
or less isolated stretches in a mature stage, separated by other 
stretches which are still submature or even young. As the 
waves cut farther into the land the mature sections increase in 
length, and finally unite when the entire shoreline has attained 
full maturity. 

Old Stage. — The old age of a shoreline of submergence does 
not differ essentially from the old age of a shoreline of emergence. 
It will be more convenient, therefore, to postpone discussion of 
this stage of development until after the youth and maturity 
of shorelines of emergence have been considered. 



REFERENCES 345 



RESUME 



In the present chapter we have passed in review those shore 
forms which characterize the different developmental stages of 
shorelines of submergence. It has been shown that by far the 
greatest variety of forms is associated with young shorelines of 
this class; while in the mature and old stages the forms are fewer 
in number, more simple in character, and more nearly like those 
in the corresponding stages of other classes of shorelines. Special 
consideration has been given to the question as to how far it is 
wise to attempt the classification of minor details of shore form 
into successive stages of development, and reasons presented in 
support of the opinion that these minor forms should not be so 
classified. The origin of the various shore forms, including cus- 
pate bars and forelands, have been examined with some care in 
order to discover which marine forces are primarily responsible 
for their development; and the conclusion has been reached 
that beach drifting under the influence of wind-formed waves is 
more potent in their construction than are tidal and other currents. 
We are now prepared to turn our attention to shorelines of emer- 
gence, and to discuss the special forms characteristic of their 
successive developmental stages. 



REFERENCES 

1. Beche, Henry T. de la. Researches in Theoretical Geology, p. 193, 

London, 1834. 

2. Dana, J. D. Geology, U. S. Exploring Expedition during the Years 

1838 to 1842 under the Command of Charles Wilkes. X, 393, 1849. 

3. Davis, W. M. Die Erklarende Beschreibung der Landformen, p. 493, 

Leipzig and Berlin, 1912. 

4. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 
") p. 704, Boston, 1909. 

5. Gilbert, G. K. The Topographic Features of Lake Shores. U. S. 

Geol. Surv., 5th Ann. Rept. P. 92, 1885. 

6. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 242, 1899. 

7. Hind, H. Y. Report on the Preservation and Improvement of Toronto 

Harbor. Canadian Journal. II, Supplement, pp. 1-14, 1854. 

8. Fleming, Sanford. Toronto Harbor — Its Formation and Preserva- 

tion. Canadian Journal, II, 105-107, 223-230, 1853. 

9. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

p. 715, Boston, 1909. 



346 DEVELOPMENT OF THE SHORELINE 

10. Johnson, Douglas W. and Reed, W. G. The Form of Nantasket 

Beach. Jour, of Geol. XVIII, 162-189, 1910. 

11. Duane, J. C, et at. Repor of Board of Engineers (on Deepening 

Gedney's Channel Through Sandy Hook Bar, New York). 48th 
Congress, 2nd Session, House of Representatives. Executive Docu- 
ment No. 78, p. 12, 1885. 

12. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 213, 1899. 

13. Richthofen, F. von. Fuhrer fur Forschungsreisende, p. 181, Hannover, 

1901. 

14. Hentzschel, Otto. Die Hauptkiistentypen des Mittelmeers, p. 52, 

Leipzig, 1903. 

15. Shaler, N. S. Beaches and Tidal Marshes of the Atlantic Coast. 

National Geogr. Monogr. I, p. 153, 1895. 

16. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 179, 1899. 

17. Branner, J. C. Stone Reefs on the Northeast Coast of Brazil. Bull. 

Geol. Soc. Amer. XVI, 1-12, 1905. 
Branner, J. C. The Stone Reefs of Brazil: Their Geological and Geo- 
graphical Relations, with a Chapter on the Coral Reefs. Bull. Mus 
Comp. Zool. XLIV, 1-285, 1904. 

18. Beaufort, Francis. Karamania, or a Brief Description of the South 

Coast of Asia Minor and of the Remains of Antiquity, pp. 174-182, 
London, 1817. 

19. Cold, Conrad. Kusten-Veranderungen im Archipel, p. 31, Marburg, 

1886. 

20. Gilbert G. K. Lake Bonneville. U. S. Geol. Surv. Mon. I, p. 55, 

1890. 

21. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 189, 1899. 

22. Pianigiani, O. Dizionario Etimologico della Lingua Italiana. II, 

1438, 1907. 

23. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 195, 1899. 

24. Johnson, D. W. and Reed, W. G. The Form of Nantasket Beach. 

Jour, of Geol. XVIII, 162-189, 1910. 

25. Hobbs, W. H. Earth Features and Their Meaning, p. 241, New York, 

1912. 

26. Fleming, Sanford. Toronto Harbor — Its Formation and Preserva- 

tion. Canadian Jour. II, 227, 1853. 

27. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences XXXIV, 217, 218, 1899. 

28. Gulliver, F. P. Cuspate Forelands. Bull. Geol. Soc. Amer. VII, 203, 

1896. 

29. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 191, 1899. 

30. Ibid., p. 192. 

31. Ibid., pp. 193, 199. 



REFERENCES 347 

32. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts, and 

Sciences. XXXIV, 204-226, 1899. 

33. Ibid., pp. 174, 178, 183, 216. 

34. Ibid., pp. 177, 192, 216. 

35. Tarr, R. S. Wave-formed Cuspate Forelands. American Geologist. 

. XXII, 1-12, 1898. 

36. Woodman, J. E. Shore Development in the Bras d'Or Lakes. Ameri- 
£ can Geologist. XXIV, 329-342, 1899. 

37. Wilson, A. W. G. Shoreline Studies on Lakes Ontario and Erie. Bull. 

Geol. Soc. Amer. XIX, 493, 1908. 
Wilson, A. W. G. Cuspate Forelands Along the Bay of Qumte. Jour, 
of Geol. XII, 111, 1904. 

38. Philippson, Alfred. Uber die Kustenformen der Insel Riigen. Ver- 

handl. d. Naturhist. Vereins XLIX, 63-72, 1892. 

39. Comstock, F. N. An Example of Wave Formed Cusp at Lake George, 

N. Y. Amer. Geologist. XXV, 192, 1900. 

40. Wheeler, W. H. The Sea Coast: Destruction: Littoral Drift: Pro- 
0> tection, p. 38, London, 1902. 

41. Gilbert, G. K. The Topographic Features of Lake Shores. U. S. Geol. 

Surv. 5th Ann. Rep., p. 85, 1885. 

42. Ibid., p. 86. 

43. Abbe, Cleveland. A General Report on the Physiography of Mary- 

land. Maryland Weather Service. I, 99, 1899. 

44. Davis, W. M. Die Erklarende Beschreibung der Landformen, pp. 

505-506, Leipzig and Berlin, 1912. 

45. Gulliver, F. P. Cuspate Forelands. Bull. Geol. Soc. Amer. VII, 

407-410, 1896. 

46. Davis, W. M. Die Erklarende Beschreibung der Landformen, pp. 

475-477, Leipzig and Berlin, 1912. 



CHAPTER VII 

DEVELOPMENT OF THE SHORELINE (Continued) 

B. SHORELINES OF EMERGENCE 

Advance Summary. — The method of treatment followed in 
the preceding chapter is here applied to shorelines of emergence. 
Features characteristic of the youth, maturity and old age of 
shorelines of this class are described, and special emphasis placed 
upon those forms which for any reason merit extended consid- 
eration. Thus the origin of the offshore bar is quite fully dis- 
cussed, and new evidence presented to test conflicting theories. 
The history of tidal inlets is traced in some detail, and in view 
of their behavior modifications of the current explanations of 
offshore bar development are suggested. It is shown that there 
exists a significant relationship between the positions of head- 
lands to which some offshore bars are attached, the direction of 
longshore currents, the distribution of inlets, the width of lagoon 
and the extent of lagoon filling; and an explanation of this in- 
teresting relationship is offered. The effect of coastal subsidence 
and coastal elevation upon the history of the offshore bar and 
lagoon are discussed, and the fallacy of the theory that offshore 
bars are an evidence of coastal subsidence is exposed. Such an 
account is given of the changes to which offshore bars, tidal 
inlets and lagoons are commonly subject, as will, it is hoped, 
prove of value to the harbor and marine engineer as well as to 
the geographer and geologist. 

Initial Stage. — When a sea-bottom or a lake-bottom emerges 
from beneath the water, either because of an uplift of the land 
or a sinking of the water surface, the new shoreline may be 
called a "shoreline of emergence." The essential characteris- 
tics of such a shoreline depend upon the fact that the bottoms 
of lakes and seas are not subjected to the river erosion which 
roughens land surfaces, but on the contrary are made even 
smoother by the continual deposition of matter brought into 
these quiet water bodies. If the plain of deposition emerges, 

348 



INITIAL STAGE 349 

the water surface coming to rest against any portion of the 
nearly level plain surface, will give a straight. or nearly straight 
shoreline. 

In case the bottom of a sea or lake represents a rugged land 
area but recently depressed, and the emergence occurs before 
deposition has had an opportunity to bury the inequalities and 
produce a smooth subaqueous surface, then the emergence of 
the rugged bottom will give an irregular shoreline. Evidently 
the dominant features of this shoreline were determined by the 
submergence of the original hills and valleys, and not by the later 
partial emergence which was insufficient to change the type of 
the shoreline already existing. For purposes of classification and 
study such a shoreline must be grouped with shorelines of sub- 
mergence, the partial emergence being of secondary importance 
only. Thus the coast of Maine is an excellent example of a 
shoreline of submergence, although a moderate amount of emer- 
gence succeeded the submergence which gave the shore its essen- 
tial characters. 

A subaqueous plain of deposition normally has a surface 
gently inclined away from the shoreline. After emergence, 
therefore, we should expect to find shallow water seaward from 
the new shoreline of emergence, the offshore slope being very 
gradual This is one of the essential characteristics of the initial 
stage of a shoreline of emergence; and since the shallowness 
of the water prevents the access of large waves to the shore, the 
early stages of development of such a shoreline are much affected 
by this feature. 

During storms large waves break far out to sea, sometimes 
encountering water too shallow for their propagation several 
miles from the shoreline. Smaller waves reach the shore and 
begin their attack upon the land. A cliff is cut, which, because 
of its small size, is sometimes called a nip in the edge of the land. 
In the manner fully explained on previous pages the bench in 
front of this small cliff is gradually deepened and the cliff pushed 
inland, increasing in height as it is cut farther into the upward 
sloping coastal plain. In the meantime the large waves break- 
ing farther seaward are cutting into the sea-bottom, and while 
part of the resulting debris is carried out to deeper water, another 
part is thrown upon the landward edge of the submarine cut, 
to form a submarine bar roughly parallel with the shoreline. 



350 DEVELOPMENT OF THE SHORELINE 

Where emergence is gradual, as is perhaps usually the case, the 
bar may form before the mainland is appreciably cliffed by 
wave action, and the nip observed later may then be wholly 
the work of lagoon waves. When the bar has been built upward 
to the water surface, the shoreline of emergence may be said to 
have passed its initial stage and to have entered that of youth. 

Young Stage. — As soon as the submarine bar lying offshore 
has been raised above the surface of the water, we can distin- 
guish an outer and an inner shoreline; the first bordering the 
seaward side of the offshore bar, or barrier beach as it is often 
called, while the second is the original shoreline, now character- 
ized by the low cliff or nip bordering the edge of the mainland. 
Between the mainland and the bar lies a lagoon, on whose sur- 
face small waves only can be generated, both because of the 
shallow depth and the comparatively short stretch of open 
water exposed to wind action. Inasmuch as the offshore bar 
is the most striking feature of the young shoreline of emergence, 
we may appropriately consider the precise method of its devel- 
opment somewhat fully. 

Offshore Bar. — Various theories have been offered to ac- 
count for the production of a narrow bar lying parallel to, but 
some distance from, a gently sloping sandy shore. One writer 
has even gone so far as to deny their marine origin. Bryson 1 , 
writing in 1888, considered that the offshore bars along the 
south side of Long Island had been produced by subglacial 
streams, and naively remarks: " These beaches have generally 
been held to be of marine origin, but this idea is being aban- 
doned." In a later paper 2 he states that the bars are really 
kames. We can at least agree with his admission that " this 
hardly seems possible." Schott 3 tried to explain the remark- 
able offshore bar bordering the north shore of Yucatan as the 
product of outward pressing land waters meeting the resistance 
of the sea. 

Louis Agassiz 4 suggested that at least along the coast of 
the southern United States the offshore bars of sand rested 
upon pre-existing coral reefs. Merrill 5 was convinced that 
these bars were " formed under water by wave and current 
action," but experienced difficulty in accounting for the appear- 
ance of their crests above the surface of the water. He solved 
the problem by assuming an elevation of the sea-bottom which 



YOUNG STAGE 351 

" brought these sand-bars above water into a horizon of aeolian 
action. Once above the sea, the beaches would maintain their 
existence." McGee 6 , on the other hand, seems to have regarded 
the presence of offshore bars and keys as a proof of coastal sub- 
sidence, the sea having encroached upon the land so rapidly as 
a consequence of the sinking movement that the bars were left 
behind. This implies the belief that such bars begin to form 
at the edge of the mainland, which is clearly the conception of 
Ganong 7 who writes as follows concerning small bars off the 
coast of New Brunswick: " They no doubt formed against the 
margin of the flat upland as ordinary shore beaches. But the 
steadily progressing subsidence carried the land beneath the sea 
faster than the beaches, whose rate of inward movement is 
largely determined by the rate of erosion of the protecting head- 
lands, could follow; hence the lagoons were formed." While 
the forms described by Ganong should perhaps be classed as 
bay bars, the principle involved does not differ from that in the 
case of the offshore bars called " keys " by McGee. It would 
seem that a similar idea as to the origin of offshore bars has been 
entertained by David White and C. A. Davis, as it is otherwise 
difficult to understand their belief that such bars should be re- 
garded as proofs of coastal subsidence 8 . 

One of the best accounts of offshore bars is of earlier date 
than any of the discussions mentioned above, having been 
published by Elie de Beaumont 9 in 1845. In his " Lecons de 
Geologie Pratique " this keen observer not only describes the 
bars at much length and explains how wave action on a shallow 
bottom removes part of the material and heaps it up in a ridge 
parallel to the shore, but also states that this change involves a 
readjustment of the submarine slope to bring it into closer 
harmony with the movements of the water. In other words, 
he recognizes the effort of the sea to establish a profile of equi- 
librium, and that the offshore bar is one result of this effort. 

Shaler 10 emphasizes the relation of offshore bars to shorelines 
of emergence, and assumes an uplift of the continental shelf as 
the first step leading to the formation of such a bar. The 
second step is considered by him to be shallowing of the offshore 
zone by deposition of debris eroded from the margin of the 
land, and other debris moved landward by the friction of the 
waves upon the bottom farther seaward. Not until this shal- 



352 DEVELOPMENT OF THE SHORELINE 

lowing has occurred does he imagine bar formation to begin. 
Storm waves then break at a considerable distance from the 
land, and drop the debris they were moving landward, thus 
building a ridge parallel with the shore which is permanently 
preserved in case it rises above the surface of the sea. 

Gilbert 11 and Russell 12 do not appear to make a clear dis- 
tinction between bay bars and offshore bars. Thus Gilbert's 
description of what he terms " the barrier " would seem to apply 
to offshore bars formed in gradually shallowing water. This 
interpretation is sustained by the fact that he compares with 
" the barrier," those " low ridges of sand or gravel running par- 
allel to the shore and entirely submerged " which can be traced 
continuously for hundreds of miles along the shores of Lake 
Michigan, but whose origin is uncertain 13 . On the other hand, 
the bay bar at Stockton, Utah, is called both a " bay bar " and 
a " barrier 14 ; " and the dependence upon shore drift ascribed 
to " barriers " would seem more characteristic of bay bars than 
of offshore bars. Russell 15 describes the formation of " barrier- 
bars " in terms which recall Gilbert's description of " the barrier "; 
and compares them with the submerged ridges paralleling the 
Lake Michigan shores. But Russell's illustration of " barrier- 
bars" shows ordinary bay bars closing the mouth of a small bay. 

Assuming that Gilbert and Russell intended their descriptions 
to apply equally to offshore bars and bay bars, and taking 
Gilbert's description for examination as being the more complete 
of the two, we may next note the essential elements of this theory 
of offshore bar formation. According to Gilbert the material 
of which the bar is composed consists of "shore drift " which 
is being moved parallel to the coast by longshore currents. On 
a gradually shallowing shore " the waves break at a consider- 
able distance from the water margin. The most violent agita- 
tion of the water is along the line of breakers; and the shore 
drift, depending upon agitation for its transportation, follows 
the line of the breakers instead of the water margin. It is 
thus built into a continuous outlying ridge at some distance 
from the water's edge. . . . The barrier is the functional 
equivalent of the beach. . . . The beach and the barrier are 
absolutely dependent on shore drift for their existence. If the 
essential continuous supply of moving detritus is cut off, . . . 
the structure (is) demolished by the waves which formed it 16 ." 



YOUNG STAGE 



353 



r 




> 

o 

ci 



354 DEVELOPMENT OF THE SHORELINE 

Davis follows Shaler in relating the offshore bar to a shore- 
line of emergence, but does not admit the necessity of shallowing 
by deposition before bar formation can commence. He follows 
de Beaumont and Shaler in deriving the material of the bar 
from the offshore bottom, and disagrees with Gilbert who re- 
gards the material of the bar as shore debris in process of trans- 
portation parallel to the shore; for while Gilbert believed long- 
shore transportation to be absolutely necessary, Davis states 
his conviction that offshore bars " might be developed essen- 
tially under the control of on- and offshore action alone 17 ." 
The successive stages in the development of an offshore bar 
are described by Davis at some length in his " Erklarende 
Beschreibung der Landformen," where the discontinuous char- 
acter of the bar during its initial stage, and the progressive 
narrowing of tidal inlets to a limiting size determined by an 
ultimate equilibrium between tidal and longshore currents, are 
emphasized 18 . Shaler 19 , on the other hand, believed that the 
offshore bar had great continuity when first formed and that 
the so-called tidal inlets were really " outlets " formed by the 
bursting through of land waters dammed off from the sea by 
the bar. 

Agassiz's theory, connecting offshore sand bars with coral 
reefs, may be dismissed on the ground that records of numerous 
wells drilled on the offshore bars along the coast of the south- 
eastern United States fail to show the presence of such a reef 
below the sandy surface. While it is true that coral limestone 
sometimes underlies a ridge of beach or dune sand, as for ex- 
ample in the Florida keys, such a relation is not typical for the 
offshore bars from Long Island and New Jersey to Texas. Both 
theoretical considerations, and direct observations of small off- 
shore bars raised above the level of lakes by wave action alone, 
justify us in rejecting Merrill's contention that an elevation of 
the sea-bottom is necessary to bring the bar crest above water. 
Equally untenable is the position of McGee, Ganong, White, 
and C. A. Davis that a subsidence of the sea-bottom is necessary 
for the development or maintenance of offshore bars. As this 
conclusion is of much importance in connection with the problem 
of recent coastal subsidence, we will return to it in a later para- 
graph. That portion of Shaler's statement which calls for offshore 
deposition of wave-eroded debris before bar formation can begin, 



YOUNG STAGE 355 

seems unnecessary; for simple uplift of a very gently sloping sea- 
bottom will produce the shallow offshore bottom which alone is 
necessary for the application of the theory of bar formation which 
he supports. The opinion that tidal inlets are really outlets 
formed by land waters bursting through a formerly more or less 
continuous bar, an opinion expressed by others 20 besides Shaler, 
is not supported by the evidence. Inlets are continually being 
opened through offshore bars and through bay bars which are 
already so discontinuous as to make the damming of land water 
an impossibility. The forcing of the opening from the seaward 
side by wave attack has repeatedly been observed; and the 
sudden rise of water in the lagoon immediately after the breach- 
ing of the bar, as at Scituate during the storm of 1898, proves 
that the sea, and not the land waters in the lagoon, may be the 
higher. Occasional inlets may be opened from the landward 
side; but as a rule the beach is forced by the waves of the sea. 
The theories of de Beaumont and Gilbert seem most worthy 
of critical consideration. It does not seem necessary to rely 
upon ordinary " shore drift " either for the initiation or main- 
tenance of offshore bars, as is required by Gilbert's theory. 
There is, to be sure, abundant evidence of longshore transporta- 
tion of debris on the seaward side of most offshore bars; but it 
seems impossible to assign the vast volumes of material in the 
great bars along the south Atlantic and Gulf coasts of the United 
States to a source at one or the other end of such bars where 
they may connect with the mainland, or may recently have done 
so. The supply of debris from headlands is so small, and the 
loss of material from attrition under wave action along the 
face of the bars must in the aggregate be so large, that notwith- 
standing the impossibility of making a reliable comparison be- 
tween these two factors, one is impressed with the probability 
that the bars would suffer rapid destruction were some other 
source of supply not available. An adequate source, both for 
the initial building of the bars and for their maintenance during 
a slow landward migration, is furnished by the shallow sea- 
bottom; and the on- and offshore action of waves is alone 
sufficient to excavate this material and build it into bars. That 
some material is also furnished by longshore transportation 
from the bases of cliffed headlands, and that material eroded 
from the sea-bottom suffers longshore transportation, is not to 



356 DEVELOPMENT OF THE SHORELINE 

be doubted. Such action must, however, be regarded as inci- 
dental and not vital to offshore bar formation. 

Deductive Study of Offshore Bar Profiles. — The fact that Gil- 
bert's theory of offshore bar formation does not imply erosion 
of the sloping sea floor, whereas de Beaumont's theory requires 
such erosion, suggests that the difference in profiles expectable in 
the two cases might enable one to determine which of these two 
most promising theories is best able to explain existing offshore 
bars. In other words, it occurred to the writer that the actual 
profiles of present-day offshore bars should clearly indicate the 
effects of extensive bottom erosion if de Beaumont's theory be 
correct, whereas such pronounced evidence of bottom erosion 
should be lacking if the bars formed according to Gilbert's 
theory. I therefore suggested this problem to Miss Bertha M. 
Merrill, a graduate student in physiography at Columbia Uni- 
versity, as one which might yield tangible results. In the follow- 
ing paragraphs I have, with her permission, drawn freely upon 
her report of profile studies. 

It may be noted that de Beaumont's theory does not ex- 
clude the possibility of some longshore transportation of debris 
by current action, although it necessarily implies that such 
action must be of minor importance. Debris cut from the 
original sea-bottom is sufficient to form the bar, and is assumed 
to be the principal source of supply. Gilbert's theory would 
seem on first reading to exclude all erosive action .of onshore 
waves; but it is doubtful whether that author would altogether 
deny a minor role to debris eroded from the sea-bottom by the 
waves, and by them contributed to the growing bar. The 
essence of Gilbert's theory is that the bar absolutely depends 
for its existence upon, and is therefore largely composed of, 
debris brought from a distance by longshore currents. It would 
appear, therefore, that the profiles established by either of the 
two methods of bar formation operating alone might be slightly 
modified by the minor co-operation of the other method; but 
that such modifications would be so slight as not materially to 
change the essential nature of the profile characteristic of each 
method. 

It will be convenient to consider first the profiles expectable 
on the basis of Gilbert's theory. Figure 90 shows the profile 
of a partially emerged coastal plain near the shore of which a 



YOUNG STAGE 



357 



bar (6) has been built upon the uneroded sea-bottom through 
deposition by longshore currents. Because the bottom has not 
been eroded, the projection of the sea-bottom slope {ss') will in- 
tersect the sealevel surface at the inner edge of the lagoon (I). 
Even if the land area be dissected subsequent to uplift, the pro- 




Fig. 90. 

jection of the sea-bottom slope will still intersect the sealevel 
surface at the inner edge of the lagoon, although it will no longer 
coincide, as in the initial stage, with the land surface. 

In case the sea-bottom is aggraded in the vicinity of the bar, 
but decreasingly so seaward from the bar, the projection of the 




aggraded sea-bottom slope (ss\ Fig. 91) will intersect the sea- 
level surface seaward from the inner edge of the lagoon. 

We may imagine a third case in which the sea-bottom is 
aggraded in the vicinity of the bar, but to an increasing extent 
as one goes seaward. Then the projection of the aggraded sea- 




Fig. 92. 

bottom slope (ss', Fig. 92) would intersect the sealevel surface 
landward from the inner edge of the lagoon. This case is highly 
improbable, for, according to Gilbert's theory, the bar is built 
up in the zone of maximum wave agitation. This zone occurs 
where the greatest number of waves expend their maximum 
energy upon the sea-bottom. Seaward from the bar, agitation 
is less because fewer waves are large enough to break there. 



358 



DEVELOPMENT OF THE SHORELINE 



Since deposition is dependent upon, ana proportional to, the 
amount of agitation, deposition decreases gradually away from 
the bar. Hence it is difficult to conceive an^area of maximum 
deposition at b, an area of little or no deposition at s, and an 
area of increasing deposition at s'. 

We conclude that in all profiles expectable according to the 
Gilbert theory, the sea-bottom slope projected will intersect the 
sealevel surface at or seaward from the inner margin of the lagoon. 

Let us next consider the profiles which might characterize 
offshore bars constructed according to the de Beaumont theory. 
Figure 93 shows such a profile in which the original slope of 
a partially emerged coastal plain {cc') has been eroded by the 




waves to produce a new sea-bottom (ss f ), while a portion of the 
debris has been thrown up into an offshore bar (6). It appears 
that the projection of the sea-bottom slope (ss f ) will intersect 
the sealevel surface some distance landward from the inner 
margin of the lagoon. Such a case would occur when all the 
material cut from the sea-bottom was either piled up in the bar 




Fig. 94. 



or carried too far seaward to affect this portion of the profile. 
A more probable profile is that represented in Figure 94, which 
shows the sea-bottom aggraded by deposition of part of the 
erosion products (s f ) seaward from the zone of maximum wave 
attack (s). Again the projection of the sea-bottom slope (ss') 
will intersect the sealevel surface some distance landward from 
the inner margin of the lagoon. 



YOUNG STAGE 



359 



In both the above cases we have imagined that the angle of 
slope of the initial coastal plain and its seaward continuation is 
greater than the angle of slope of the newly fashioned sea- 
bottom. It is conceivable, however, that the original slope of 
the coastal plain might be so extremely gentle that the new 
submarine slope would be appreciably steeper. Such a condi- 
tion is represented in Figure 95, from which it will be seen that in 
cases of this kind the projection of the sea-bottom slope (ss') 




Fig. 95. 

may intersect the sea-level surface at or seaward from the inner 
margin of the lagoon. The situation would be the same, of 
course, were the more steeply sloping sea-bottom a surface of 
aggradation, as shown in Figure 96. It would seldom happen 
that the projected sea-bottom slope would emerge exactly at 




Fig. 96. 



the inner margin of the lagoon. It should be noted that in 
cases of this kind the very gentle initial offshore slope will 
cause waves to break far from land, and the resulting bar will 
enclose a lagoon of exceptional width. 

We conclude, therefore, that in profiles expectable according 
to the de Beaumont theory the sea-bottom slope projected will 
intersect the sealevel surface landward from the inner margin of 
the lagoon, except in those cases where the original surface 
slope is exceptionally low. 

We may summarize the results of the deductive study of 
profiles as follows: 



360 DEVELOPMENT OF THE SHORELINE 

Class I. If the sea-bottom slope projected intersects the 
sealevel surface at the inner margin of the lagoon, the offshore 
bar was probably formed according to Gilbert's theory. 
I Class II. If the sea-bottom slope projected intersects the 
sealevel surface landward from the inner margin of the lagoon, 
the bar was probably formed according to de Beaumont's 
theory. 

Class III. If the sea-bottom slope projected intersects the 
sealevel surface seaward from the inner margin of the lagoon, 
the bar may have been formed according to either theory; 
where the seaward slope of the land is at all pronounced, prob- 
abilities favor the Gilbert theory; where the coast is unusually 
flat and the lagoons very broad, the de Beaumont theory may apply. 

Comparison of Actual Profiles of Offshore Bars. — To test the 
merits of the two theories, eighteen profiles were constructed for 
coasts having well-developed offshore bars. For this purpose the 
United States Coast and Geodetic Survey charts and the United 
States and Dutch Hydrographic charts were used. In order to 
eliminate from the profiles local and minor irregularities of the 
submarine slope, all the soundings within a zone of certain width, 
varying from five to seven miles according to circumstances, 
were projected on a single vertical plane normal to the shore- 
line, and the mean curve taken as the profile for that zone. Be- 
cause such bars appear in great perfection off our own Atlantic 
and Gulf coasts, and because these coasts have been thoroughly 
charted, a majority of the profiles were taken from these regions. 
The others were constructed across bars of the North Holland, 
German, and Venetian coasts. 

The results for each case, with appropriate comments, are 
briefly presented below: 

Figure 97, Profile through the Gulf of Venice. From United 
States Hydrographic Chart, Adriatic Sheet I. The sea-bottom 
slope projected (broken line) intersects the sealevel surface land- 
ward from the inner margin of the lagoon, thus placing the 
profile in Class II. 

Figure 98, Profile through the Kurische Nehrung and Haff 
on the Baltic coast. From United States Hydrographic Chart, 
Baltic Sheet II. The sea-bottom slope projected again inter- 
sects the sealevel surface landward from the inner margin of 
the Haff, showing that this profile also belongs in Class II. 



YOUNG STAGE 



361 




II 



» a 

jS 5 



CO 



> 




h _ OQ 



> 



!«3 



I 

"8 

3 
o 



362 DEVELOPMENT OF THE SHORELINE 

Figures 99, 100. 101, Profiles through the Terschelling, Ameland, 
and Vlieland bars on the North Holland coast. From Dutch 
Hydrographic Charts Nos. 205 and 224. The profile through 
the Terschelling bar clearly belongs in Class II. In the case of 
the Ameland and Vlieland bars, too little of the sea-bottom slope 
is shown on the chart to serve as a basis for projection; but 
from the relation of these areas to the Terschelling area, and 
from other data for the sea-floor topography, it is known that 
both profiles belong in Class II. 

Figures 102, 103, Profiles through the Cape Hatteras bar, North 
Carolina coast. From United States Coast Survey Charts Nos. 
1232 and 1229. The coast is " an excessively flat plain," and 
the lagoon exceptionally wide. Both profiles belong in Class III. 

Figure 104, Profile through Currituck Beach, northern coast of 
North Carolina. From United States Coast Survey Chart No. 
1229 11 . This part of the coast is less flat and the lagoons corre- 
spondingly narrower than further south where the profiles shown 
in Figures 102 and 103 were taken. The profile through Curri- 
tuck Beach unquestionably belongs to Class II, as shown by 
Figure 104. 

Figure 105, Profile through Assateague Island bar, Maryland. 
From United States Coast Survey Chart No. 1220. The profile 
appears to show local submarine bars, possibly of the low and 
ball type discussed later, and clearly belongs to Class II. 

Figures 106, 107, Profiles through the offshore bar of the New 
Jersey coast, near Barnegat Inlet. From United States Coast 
Survey Charts Nos. 121 and 122. Both profiles belong in 
Class II. 

Figure 108, Profile through Fire Island bar, south coast of 
Long Island, New York. From United States Coast Survey 
Chart No. 1214. The profile belongs in Class II. 

Figure 109, Profile through Galveston Bay and Bolivar bar, 
Texas coast. From United States Coast Survey Chart No. 
204. The profile belongs in Class II. 

Figure 110, Profile through Matagorda Bay and bar, Texas 
coast. From United States Coast Survey Chart No. 207. The 
profile belongs in Class II. 

Figures 111, 112, 113, and 114. Profiles through Laguna Madre 
and Padre Island bar, Texas coast, in latitudes 27° 25', 26° 10', 
26° 45' and 26° 25' respectively. From United States Coast 



YOUNG STAGE 



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DEVELOPMENT OF THE SHORELINE 




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YOUNG STAGE 365 

Survey Charts Nos. 210, 211, and 212 respectively. The pro- 
files are arranged according to increasing breadth of lagoon. 
The first three clearly fall in Class II; and the fourth, where 
the lagoon is exceptionally broad, appears to do so, although it 
closely approaches the conditions of Class I. < 

Summarizing the results obtained from the foregoing exam- 
ination of profiles through offshore bars, we note that out of 
eighteen profiles studied, sixteen fall in Class II, although one 
of these approaches closely the conditions of Class I. The two 
remaining profiles fall in Class III. Both the two profiles of 
Class III and the profile closely approaching Class I occur off 
very flat coasts where the lagoons are exceptionally wide, as 
would be expected were the bars formed according to the theory 
of de Beaumont. In other words, fifteen of the profiles cer- 
tainly fall in Class II, indicating that the bars were formed 
according to the de Beaumont theory; while the remaining 
three profiles, explicable according to either the Gilbert or the 
de Beaumont theory, show features suggesting that they also 
were formed according to the de Beaumont theory. 

It might be argued that the bars first formed according to 
the Gilbert theory and were then pushed landward, the waves 
cutting into the sea-bottom and adding part of the erosion 
products to the bars. This would be to assume an initial stage 
of bar formation the validity of which could not be tested by 
appropriate facts of observation, and to admit that the bars as 
we now see them owe their existence, in part at least, to the 
process outlined by de Beaumont and more fully described by 
Davis. Under these circumstances it is perhaps more reasona- 
ble to accept the de Beaumont theory of bar formation, not for- 
getting, however, that longshore transportation of debris is an 
accessory process of very great importance. 

1 Development of the Offshore Bar. — In tracing the development 
of an offshore bar we may therefore imagine a gradually shallow- 
ing sea-bottom on which small waves break at the initial shore- 
line and excavate a marine cliff and bench, while large waves 
break farther out and proceed to excavate the same forms in the 
offshore bottom. Along the outer zone part of the excavated 
material is deposited just landward of the breakers, in less agi- 
tated water; that is, on the crest of the submarine cliff. As the 
waves excavate deeper and farther landward the deposit on the 



366 DEVELOPMENT OF THE SHORELINE 

summit of the submarine cliff increases in volume until a sub- 
marine bar of significant height, and indefinite length parallel 
to the inner shoreline, is formed. Further growth brings the 
crest of the bar above water at irregular intervals, giving a chain 
of islands separated by wide spaces of shallow water covering 
the still submerged portions of the crest. With continued exca- 
vation along the seaward face of the bar and addition to its crest, 
the islands increase in number and in length, progressively nar- 
rowing the water spaces between them and ultimately coalescing 
to a greater or less extent to form a more nearly complete barrier 
between the open sea and the shallow lagoon 

Tidal waters which formerly ebbed and flowed across the 
wholly submerged bar with little hindrance, now find themselves 
confined to a limited number of increasingly narrower passage- 
ways between the ever lengthening above-water portions of the 
bar. As the openings decrease in size, the tidal currents (in- 
cluding the all-important hydraulic currents generated by tidal 
action) flowing into and out of the lagoon increase in velocity. 
They compensate in some measure for the increasingly restricted 
breadth of their passageways by cutting deeper channels across 
the still submerged portions of the bar; and it seems probable 
that this process may often be carried so far that tidal channels 
are cut clear through the bar and into the original sea-bottom 
below. 

As the submarine bar approaches the surface it comes more 
and more under the influence of the local wind-generated waves 
which affect the water to a shallow depth only. As a majority 
of these waves strike the seaward face of the bar obliquely, 
beach drifting alongshore becomes increasingly important, and 
soon is the dominant factor in the narrowing of tidal inlets. 
No longer are the above-water portions of the bar extended and 
the inlets narrowed mainly by simple vertical upbuilding of the 
still submerged parts of the bar. Instead, the debris eroded 
from the bottom and cast up against the face of the bar is at- 
tacked by oblique wind-made waves and transported laterally 
to be deposited at the ends of the elongated islands, thereby 
increasing their length and narrowing the inlets. This action 
is directly opposed to that of the tidal currents which pass in 
and out of the inlets and endeavor to keep them open by re- 
moving material deposited by the longshore currents. So long 



YOUNG STAGE 367 

as the longshore action is dominant, the inlets continue to 
narrow; but this very narrowing, by confining the tidal currents 
to smaller and smaller cross sections, progressively increases 
their velocity. A time must come when the inlets are narrowed 
enough to give the tidal currents a strength equivalent to that 
of the longshore currents. Thereafter deposition at the margins 
of the inlets by longshore currents is followed by equivalent 
erosion through the agency of tidal currents. Equilibrium be- 
tween the two opposing forces is established, and the breadth of 
the inlets remains approximately constant. 

The required breadth may be maintained by a few compara- 
tively broad inlets, or a larger number of narrower inlets. Since 
a larger tidal range means stronger tidal currents, we should 
expect to find some relation between the range of the tide along 
a given coast and the number or size of the inlets through its 
offshore bars. Such a relation seems to exist. Thus along the 
New Jersey coast, where the tidal range is from 4 to 5 feet, in- 
lets are more frequent than along the coast of Texas where 
with a tidal range of but 1 or 2 feet one offshore bar extends un- 
broken for about 100 miles. 

Factors Controlling the Number and Breadth of Tidal Inlets. — 
It is commonly assumed that the amplitude of the tide is 
the only factor involved in determining the number and width 
of tidal inlets through offshore bars. Both theoretical con- 
siderations and field observations negative this assumption. In 
addition to the varying strength of longshore action (mainly 
beach drifting) , the volume of land water, the extent to which the 
lagoon is filled with sediment or marsh deposits, the abundance 
and rapidity with which debris is supplied, and the strength of 
storm-wave attack, are all factors o importance. With the 
same tidal range along two offshore bars, it may happen that 
longshore current action is weak on one, but vigorous on the 
other. Under such conditions the one with the weaker long- 
shore currents will have more or wider inlets. Where large 
rivers empty into a lagoon, the ebb current of the tide is greatly 
reinforced by the land waters, and will keep open inlets which 
would otherwise be narrowed or closed. As sedimentation and 
marsh growth decrease the water space of the lagoon, the volume 
of tidal waters admitted and the strength of the tidal currents is 
reduced, in consequence of which longshore currents may be 



368 DEVELOPMENT OF THE SHORELINE 

able to narrow or even close some of the inlets. If an abun- 
dance of debris is supplied to longshore currents with great 
rapidity, the closing of inlets will be more readily accomplished 
than if a smaller amount of debris is supplied very slowly. An 
inlet, once closed, might never be re-opened were it not for 
breaches made in the bar by storm-wave attack. Tidal action 
tends to keep inlets open; but, except in the case of an unusually 
high tide overflowing a low point on a bar, does not tend to pro- 
duce inlets. Impounded land water may in rare instances open 
an inlet after the manner described by Shaler; but inlets are 
more commonly re-opened during exceptional storms by vigor- 
ous wave erosion. A bar exposed to the waves of an occasional 
great storm may thus be breached, where one less exposed would 
remain intact. 

On the other hand, it matters little how many inlets may be 
opened by the waves, longshore currents will soon close all 
except those kept open by tidal currents reinforced by outflow- 
ing land waters. If the tidal range is such as to generate currents 
capable of maintaining two inlets of a given breadth through a 
certain bar, and storm waves cut two additional inlets, the tidal 
waters will for a time flow through the greater number of open- 
ings with decreased velocities. Longshore currents will therefore 
dominate the tidal currents at the inlets, until deposition has 
narrowed all of the inlets, or closed two of them (often the older 
ones), leaving the other. two of the required breadth and thereby 
re-establishing a condition of equilibrium. Or, if a storm drives 
waves obliquely upon a coast in such manner as greatly to accel- 
erate the longshore transportation of debris, all the inlets through 
a bar may be closed by excessive deposition in spite of tidal cur- 
rents Once the inlets are closed, the tidal currents cease to 
exist; and the inlets will remain closed until storm waves or some 
other agency makes new breaches through the bar. In general 
we may say that waves tend to make inlets, tidal currents to 
preserve them, and longshore currents to close them. 

Theory of Tidal Inlet Distribution. — That the supply of debris 
brought by longshore currents may be more important than 
differences of tidal range in determining the number of inlets 
through a bar, is apparent from a study of certain offshore bars 
which are supplied with debris derived from headlands to which 
the bar is at one end attached. Let us deduce the conditions 



YOUNG STAGE 369 

which theoretically should characterize offshore bar and lagoon 
development when the bar is attached to a headland, and long- 
shore currents move from the headland toward the further ex- 
tremity of the bar. 

In the first place, it is evident that while wave currents may 
remove much material from the face of the bar and transport it 
seaward to deeper water, near the headland the loss may be 
more or less completely made good by new debris brought from 
the adjacent source of supply by longshore currents. The effect 
of this accession of debris is two-fold: the bar withstands the 
normal tendency of the waves to drive it landward since the 
waves have all they can do to take care of the new material con- 
tinually being added to its face; and for the same reason the 
waves are less apt to cut inlets through the bar, while longshore 
currents utilize the abundant debris to seal up such inlets as 
may occasionally be formed. Accordingly we should expect a 
tendency for lagoons to be broad and bars to be continuous in 
the vicinity of headlands. 

Toward that end of the bar most remote from the headland, 
conditions are very different. The debris from the headland 
has been ground fine in the course of its journey, and largely 
dissipated. Wave attack expends its full energy upon a bar 
which receives little material from the distant headland to offset 
the ravages of marine erosion. Hence the bar is driven land- 
ward with greater ease, and during its retreat the waves cut 
through first here, then there, forming inlets which are not 
closed as readily as where debris is more abundantly supplied. 
Far from headlands, therefore, there should be a tendency for 
lagoons to be narrow and for bars to be broken by frequent 
inlets. 

We may deduce an interesting corollary as to conditions 
within the lagoon. Where the bar is continuous, little sediment 
from its seaward side can reach the lagoon, and that little must 
be brought in suspension by tidal waters entering by some 
distant inlet. Where inlets are abundant, more sediment can 
enter the lagoon with flood tide, even though this be the part 
of the bar most poorly supplied with debris from the distant 
headland. It must also appear that the end of the lagoon near 
the headland is least apt to have a constant salinity. At times 
the water may become nearly fresh, while high tides or tempo- 



370 DEVELOPMENT OF THE SHORELINE 

rary inlets will result in a high salt content. Such variations in 
salinity are unfavorable to the growth of either marine or fresh 
water vegetation. On the other hand, where numerous inlets 
keep the lagoon waters constantly salt, marine grasses thrive 
and contribute effectively to the filling of the lagoon. We 
conclude, therefore, that theoretically the " up-current " or 
headland end of a lagoon should be more open than the further 
end where marine sediment and marine vegetation unite to 
form a salt marsh filling. 

The Theory Tested. — If we turn now to an examination of 
offshore bars and lagoons along the Atlantic Coast, we find that 
despite the manifest possibility of other factors complicating the 
situation, there exist substantial confirmations of the theory of 
inlet formation outlined above. (In the discussion which follows 
I have drawn freely upon the results of map studies made by 
Miss B. M. Merrill, under my direction.) On the south side of 
Long Island the longshore current moves westward along an 
offshore bar (Fig. 115) which is attached at its eastern end to a 
complex headland consisting of a terminal moraine and outwash 
plain. From Southampton, where the bar really springs from 
the mainland (it barely touches it at Quogue) westward to the 
Gilgo Lifesaving Station, a distance of 54 miles, there is only 
one inlet; in the next 22 miles, to Far Rockaway, there are 
three inlets. For sake of easy comparison with the cases which 
follow, we may say that nearest the headland the inlets occur at 
the rate of 2 to 100 miles, while farther away the rate is 14 to 
100 miles. Great South Bay, the main lagoon, is wide and 
comparatively free from tide marsh in the half nearest the head- 
land, narrower and almost filled with marsh in the farther half 
where inlets are frequent. The actual conditions are precisely 
those which deduction led us to expect. 

The New Jersey coast is fringed by an offshore bar (Fig. 116) 
attached at its northern end to a headland consisting of the cliffed 
coastal plain between Long Branch and Bayhead. The longshore 
current moves southward from the headland. In the first 50 
miles there are 2 inlets, in the next 50 miles, 8 inlets. In other 
words, nearest the headland the inlets average 4 to 100 miles, 
farther away 16 to 100 miles. As in the Long Island case the 
half of the lagoon nearest the headland has the greater average 
width and the smallest amount of marsh filling. Toward the 



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Page 371 



372 DEVELOPMENT OF THE SHORELINE 

south, where inlets are frequent, we find the lagoon narrow and 
almost completely filled with marsh. In this case also the 
observed facts conform to the expectations as deduced from the 
proposed theory of inlet formation. 

Similar conditions obtain off the coast between Delaware 
and Chesapeake Bays. An irregular headland extending from 
Cape Henlopen to Bethany Beach has attached to it and ex- 
tending southward an offshore bar which continues for some- 
thing over 50 miles before the first inlet is reached, whereas in 
the next 50 miles ten inlets occur. The relation is therefore 
roughly expressed by assigning a rate of 2 inlets per 100 miles 
for the headland end of the bar, and 20 inlets per 100 miles for 
the farther end. Near the headland end we have the open 
Chincoteague Bay. Farther south the lagoon is first narrow 
and marsh-filled; but the expectable relations are then masked 
by a widening of the lagoon area possibly as the result of an 
exceptionally flat initial sea floor which permitted the bar to 
form far offshore. It should be noted, however, that even 
here the inlets are close-spaced and the lagoon area largety filled 
by marshes or mud-flats, as required by the theory. 

The Carolina coast is so complicated by the three cuspate 
bars forming Capes Hatteras, Lookout, and Fear that one might 
scarcely expect to find the relationships characteristic of simple 
offshore bars. Yet if we compare different sections of the coast 
in a broad way, ignoring local abnormalities, we seem to see the 
working of the same laws controlling cases previously discussed. 
The headland for this section is the margin of the coastal plain 
of Virginia, south of Cape Henry, and the shore currents move 
in a general north to south direction. We may recognize four 
natural subdivisions of the coast: a first section from the head- 
land to Cape Hatteras, a second between Capes Hatteras and 
Lookout, a third between Capes Lookout and Fear, and a 
fourth between Cape Fear and a point just west of Little River, 
beyond which the offshore bar seems to touch the mainland again. 
In the first section the inlets number but 2 in a distance of 
113 miles, and the lagoon attains a great width with compara- 
tively little filling. The abnormal width in parts of the first 
two sections is probably due to an exceptionally gentle slope of 
the seafloor along the Cape Hatteras axis. In the second 
section of 72 miles, there are three inlets, giving an average 



YOUNG STAGE 373 

spacing of 4 to 100 miles, and the lagoon becomes comparatively 
narrow toward Cape Lookout. In the third section the number 
of inlets increases to 9 in 100 miles, while the lagoons narrow 
still more and become much more filled with marsh deposits. 
At Cape Fear the lagoon broadens out considerably, but the 
width here is onl} T seven and one-half miles as compared to 
twelve and one-half at Cape Lookout, or thirty miles at Cape 
Hatteras. In the fourth section there are eight inlets in 40 
miles, which is equivalent to a spacing of 20 inlets to 100 miles; 
the bar is driven back nearly to the mainland, and the narrow 
lagoon is almost completely filled with marsh. Despite its com- 
plexities the Carolina case appears to meet the requirements of 
the theory. 

The Florida offshore bar is so complicated by the presence of 
hard coquina along some of its parts, by the complex cuspate 
foreland of Cape Canaveral, and by coral reefs farther south, 
that it does not properly come within the scope of our enquiry. 
If we consider the Texas coast, however, taking the Rio Grande 
delta as the headland supplying the debris, and ignoring the 
Rio Grande and Brazos Santiago openings in the immediate 
vicinity of the delta, we find an offshore bar extending north- 
ward, in the direction of what appears from sand migration to 
be the dominant longshore current, more than 100 miles before 
the first inlet is encountered. Xear the headland we have the 
Laguna Madre, broadly open, but shallow because of the very 
gentle slope of the initial sea floor. Farther north the lagoon 
proper (no account should be taken of the drowned valley bays) 
grows narrower and the proportion of marsh filling increases. 

In all of the cases described above there is a marked tendency 
for the number of inlets and the proportion of lagoon filling to 
increase, and for the width of lagoon to decrease, with increase 
of distance from headlands. This seems to confirm the theory 
that the amount of debris brought from headlands by longshore 
currents exercises an important control over the number of 
inlets through offshore bars, as well as upon the rate of bar 
retreat and lagoon filling. It should be noted, however, that 
in each case the tidal range increases from the headland toward 
the farther end of the bar, although the amount of increase 
between sections of no inlets or few inlets, and sections of numer- 
ous inlets is sometimes so slight as -to be of doubtful importance. 






374 DEVELOPMENT OF THE SHORELINE 

Both distance from headland and range of tide co-operated to 
produce the observed results, but it is believed the former factor 
is the more important of the two. 

Tidal Deltas. — The hydraulic currents generated by the tides, 
and called tidal currents in the foregoing paragraphs in conformity 
with well-nigh universal custom, produce certain features at the 
inlets which deserve brief notice. Debris brought by beach drift- 
ing or other longshore currents is seized by the inflowing or out- 
flowing current at the inlet and transported into the lagoon or 
out to sea. Most of the debris is not carried far before being 
deposited in the quieter water of the larger water-body to form 
a tidal delta. 21 The typical tidal delta is wholly submerged and 
is double, one part facing landward and representing the result 
of deposition in the lagoon by incoming currents; the other 
part facing seaward and owing its construction to deposition in 
the sea by outflowing currents. Because the seaward part of 
the delta is exposed to the action of waves and longshore cur- 
rents it is commonly stunted in its growth and margined by 
contours of simple curvature; only that portion in the lagoon is 
apt to acquire appreciable size and the lobate form of ordinary 
deltas (Fig. 117). 

migrating Inlets. — The exposure of most beaches to wave 
attack is such that longshore current action (usually beach drift- 
ing) in one direction predominates over that in the other. This 
results in a marked tendency for inlets to migrate in a certain 
definite direction — that of the dominant current. Deposition on 
that side of the opening to which longshore currents bring abun- 
dant debris tends to narrow the inlet, whereas erosion alone is 
operative on the other side. An excess of deposition on one side, 
accompanied by erosion alone on the other, must result in a lat- 
eral migration of the inlet along the bar in the direction of the 
dominant current, while the breadth of the inlet remains unim- 
paired. On the New Jersey coast south of Barnegat Inlet the 
inlets through the offshore bar migrate southward, while north 
of this point the direction of inlet migration is northward. 

The presence of a dominant current along an offshore bar 
broken by inlets results in the development of offsets and over- 
laps similar to those already described in connection with bay 
bars (Chapter VI). As these two features are fully explained in 
the connection cited, it will not be necessary to consider them at 




Page 375 



376 



DEVELOPMENT OF THE SHORELINE 



greater length here. We may simply recall in passing that the 
southern New Jersey coast appears to afford an exception to 
Gulliver's rule 22 according to which the dominant current should 
"flow from the outer curve toward the inner one" along a shore- 
line marked by offsets. Here the direction of inlet migration 
proves that the dominant current is from the northeast; but 
according to Gulliver's rule the offsets 'at the inlets north of 
Cape May would require a current from the southwest. It is 
clear that the direction of offset may be determined in certain 
cases by some force other than the dominant longshore current. 
One important consequence of inlet migration which seems 
not to have been fully recognized, will claim our attention when 




Fig. 118. — Stages in the development and retrogression of an offshore 
bar. (After Davis.) 



we come to consider the landward retrogression of the offshore 
bar. It is quite generally assumed in descriptions of this last 
process that the bar comes to repose wholly upon the deposits, 
of the lagoon or marsh as soon as it has moved landward a dis^ 
tance equivalent to its own breadth. This view is well exempli- 
fied by Figure 118, reproduced from a diagram given by Davis 
in his " Erklarende Beschreibung der Landformen 23 ". It is quite 
evident, however, that the condition represented by this dia- 
gram could only obtain where inlet migration is either wholly 
absent or takes place slowly at the^same time that bar retro- 
gression is comparatively rapid. For the migration of an inlet 
along the bar results in the complete removal of that portion 



YOUNG STAGE 377 

of the bar and its underlying deposits toward which the opening 
is moving, down to the greatest depth reached by the tidal 
channel; while deposition on the up- currant side of the inlet 
forms an essentially new bar whose base rests, not on the sur- 
face of the lagoon deposits, but upon the erosion plane formed 
by the lateral migration of the inlet. Since the inlets probably 
reach to or below the original shallow sea-bottom in a majority 
of cases, the bar to leeward of the migrating inlet will commonly 
rest on the original sea-bottom deposits. 

Inside the inlet the remains of the tidal delta left on the 
up-current or leeward side of the opening will prolong the land- 
ward side of the bar into the lagoon with a gentle slope; for just 
as successive deposits of sand on the up-current side of the inlet 
remain to form the new part of the bar, so the side of the delta 
away from which the inlet is migrating is progressively left 
behind to form a sheet of sand extending from the new bar out 
into the lagoon as a thinning wedge. If the offshore bar has a 
marsh behind it instead of an open lagoon, the result is essen- 
tially the same. Erosion will remove both the bar and the 
adjacent marsh deposits on the down-current or far side of the 
inlet, while deposition of sand on the up-current or near side 
will leave a bar resting on the eroded sea-bottom. This bar 
will be extended marshward by sand deposited along the near 
side of the tidal creek connecting with the inlet. A cross sec- 
tion through an offshore bar and marsh, after the bar had 
migrated toward the land a great distance, would in this case 
not look like stage 4 in Figure 118, as is generally assumed, but 
more like stage G in Figure 119. 

In case the bar moves landward an appreciable distance after 
one inlet has migrated past the line of the cross section and 
before the next migrating inlet has reached that line, we would 
have the conditions represented in stage F, Figure 119, where the 
marsh deposits are exposed on the seaward side of the bar. 

It is evident from the considerations just outlined that it may 
be difficult or impossible to determine how far landward from 
its original position an offshore bar has migrated. Were the 
assumed conditions of stage 4, Figure 118, commonly present after 
a considerable landward migration, the problem would be more 
simple; for soundings made through the marsh deposits would 
show an increasing depth of these deposits until the margin of 




c 


Marsh 


Lagoon 


Offshore Bar 













Tidal 



Offshore Bar 




Fig. 119. — Stages in the normal history of an offshore bar, due account 
being taken of the effect of migrating inlets. Between stages F and G 
an inlet has migrated past the zone of the cross section, producing condi- 
tions similar to those in stage C or D. 
Page 378 



YOUNG STAGE 379 

the. superposed bar was reached; and wells drilled on the bar 
would pass through a thick layer of marsh mud under the beach 
sands. On the other hand, soundings showing an increasing 
thickness of marsh deposits for some distance seaward from the 
inner shoreline, followed by a gradually decreasing thickness as 
the bar was approached (stage 2, Fig. 118), and records of wells 
on the bar showing that nothing but sand was encountered by 
drilling, would indicate that the bar was still in its original posi- 
tion. 

Unfortunately such reasoning, although frequently followed, 
at least tacitly, when offshore bars are discussed, is not valid if 
shifting inlets are involved. It is clear from Figure 119, stage G, 
that the results of soundings and the well records accepted above 
as proving no landward migration of the bar, would be obtaina- 
ble in the case of a bar which had really migrated far from its 
initial position. So also, soundings or well records might indicate 
only a slight landward progress of the bar, whereas the actual 
movement had been very great. Along the New Jersey coast, 
lines of soundings across the marshes show that beyond the axis 
of the marsh the peat and swamp muds thin out and the sandy 
bottom rises gradually toward the offshore bar. Well records 
frequently show that no marsh deposits were encountered in 
drilling, or that only small thicknesses of such deposits were 
found. Since the bar is repeatedly broken through by shifting 
inlets these facts cannot be regarded as evidence that the bar 
has changed but little from its former position, any more than 
the outcropping of small quantities of peat along the outer 
shorelines can be accepted as proof of an extensive landward 
migration of the bar. Either permanence of or marked change 
in the position of the bar must be proven, if at all, by other 
lines of evidence. 

Lagoon and Marsh. — When the offshore bar is formed there 
is enclosed a long, narrow lagoon between the bar and the inner 
shoreline, the lagoon communicating with the open sea by means 
of the tidal inlets. Comparatively quiet water in the lagoon 
favors deposition of the fine debris which is derived from three 
principal sources. The products of attrition resulting from 
wave action on the outer surface of the bar are moved to the 
tidal inlets by longshore currents and the finer part is carried 
into the lagoon by tidal currents, to be widely distributed over 



380 DEVELOPMENT OF THE SHORELINE 

the shallow bottom; all the coarse material is added to the bar 
or dropped near the inlet to form the tidal delta. Rivers may 
bring sediment from the land surface into the lagoon, depositing 
the coarser part in the form of deltas along the inner shoreline, 
and delivering the finer part to the feeble currents in the lagoon 
for wider distribution. Onshore winds blow sand from the 
beach and dunes of the bar back into the lagoon. As a rule the 
coarser sand quickly drops into the water close to the lagoon 
shore of the bar, and only the finest material is wafted far over 
the surface of the waters before dropping into them to find a 
resting place on the submarine floor. 

As material from these three sources accumulates, the bottom 
of the lagoon is built upward toward the surface. If the supply 
of fine sediment is unusually abundant the lagoon may eventu- 
ally become filled with a deposit of almost pure clay or sandy 
clay, on the surface of which grow salt marsh grasses. Prob- 
ably a more normal history would be something like that de- 
scribed by Shaler 24 in which eel-grass or other salt-water plants 
first gain foothold on the muddy bottom below low-tide level 
and aid the process of deposition by checking the currents 
passing through them. Later, as the lagoon bottom reaches 
a higher level, marsh plants are able to colonize the surface, and 
their remains may form no inconsiderable proportion of the 
completed deposit. The entire lagoon is thus ultimately filled 
with a clayey formation which includes, particularly in its upper 
portions, large quantities of vegetable matter; while its surface 
is covered with the grasses of a typical growing salt marsh. 

Retrogression of Offshore Bars. — Just as continued wave attack 
ultimately forces the recession of other shoreline features, so the 
offshore bar must be driven landward in course of time. As 
previously explained the outer shoreline of the bar may tempo- 
rarily be prograded; local disturbances of the shore profile of 
equilibrium may cause the bar to widen locally, as appears to 
be the case at Atlantic City; or general and long-continued 
excessive supply of shore debris may result in broadening a bar 
into a beach plain of great extent, such as that forming Cape 
Canaveral on the Florida coast. Occasionally after a bar is built 
the zone of bar construction is shifted so rapidly seaward that a 
broad swale or lagoon is left between the bar earlier formed and 
its later counterpart. If the swale or lagoon be occupied by 



YOUNG STAGE 381 

marsh, the first bar appears as a long ridge of dry land in the 
midst of the expanse of salt grass and water (Plate XLIV). But 
all such activities are temporary, and the time will come when 
loss of fine material from attrition and removal to deep water 
will exceed the diminishing supply of shore debris. The waves, 
relieved of the burden of excessive debris transportation, will 
then utilize their surplus energy in eroding the sea-bottom aiad 
driving the bar landward. 

Material eroded from the face of the bar, and from the sea- 
bottom below, is hurled by waves to the bar crest or even be- 
yond, and descends the black slope toward the lagoon with the 
assistance of over-wash from exceptionally high waves, and 
running water due to rainfall. This insures for the actively 
retreating bar a narrow breadth and an asymmetrical cross- 
profile, the front slope toward the sea being characteristically 
steeper than that toward the lagoon; while the lagoon shore is 
apt to show a series of rude deltas where overwash has pro- 
jected beach material into the lagoon waters. If the lagoon has 
been replaced by salt marsh, the features are essentially the same, 
except that the overwash deltas spread out upon the marsh sur- 
face (Plate XLI), while the marsh muds and peat may become 
exposed below high tide on the seaward side of the bar. 

Migrating tidal inlets tend to destroy all of the features just 
mentioned: the asymmetry of the bar profile, the overwash 
deltas, and the subjacent relation of marsh deposits to the bar. 
If the bar retreats rapidly while inlets are few and migrate slowly, 
the features described may be observed, except along that por- 
tion of the bar most recently re-formed. If the bar retreats 
slowly and intermittently, while inlets are numerous and migrate 
rapidly, the lack of symmetry and the overwash deltas may be 
poorly developed, while marsh deposits beneath the bar may be 
nearly or entirely lacking. 

Gulliver 25 considers a prograding offshore bar as character- 
istic of the youthful stage of a shoreline of emergence, while a 
retrograding bar is the distinguishing feature of " adolescence." 
The exposure of marsh deposits on the seaward side of the bar is 
necessarily relied upon as the principal proof of retrogression. 
Davis 26 defines " late youth " as the period when the bar is 
driven landward far enough to show tide-marsh turf and mud on 
the outer side of the bar. One must doubt, however, whether 



382 DEVELOPMENT OF THE SHORELINE 

it is feasible to utilize such criteria as a basis for distinguishing 
different stages of shoreline development. In the first place it 
is usually impossible to tell from a map whether an offshore 
bar is advancing or retreating, so that maps would be of little 
or no use in determining whether a given shoreline was in youth 
or in its adolescent period (late youth). This difficulty is well ex- 
emplified in Gulliver's essay, where several shorelines of emer- 
gence are arbitrarily classified as " young," although the author 
admits that they may really be adolescent; but in three cases 
we read that " the scale of the map is too small to show indica- 
tions in which direction the bar is moving," " whether advanc- 
ing or retreating the writer does not know," and " the writer 
could find no evidence as to which way it is moving." 

Even if field observations are available as an aid to classifi- 
cation, the case is little better. An offshore bar may be alter- 
nately retrograded and prograded due to changing conditions of 
equilibrium of the shore profile. It will hardly help us to assume 
that such a shoreline vibrates from youth to adolescence and 
back to youth again repeatedly. On the other hand, a bar 
which had been continuously but slowly retrograded for a long 
period of time might be erroneously assigned to the youthful 
stage in case migrating inlets removed the evidences of retro- 
gression most commonly depended upon, such as the subjacent 
marsh deposits. 

Normally an offshore bar should never prograde to any 
appreciable extent, but should retrograde from the moment of 
its initiation. Prograding implies a disturbance of normal con- 
ditions, a variation in the shore profile on one part of the coast 
due to abnormal activity of some one or more of the shore 
processes, as a result of which shore debris is supplied with 
exceptional rapidity to that part of the shore where prograding 
takes place. A possible exception to this statement is the pre- 
sumably rare case in which progressively larger and larger 
storm waves built additions to the initial bar farther and farther 
seaward. It seems unwise to adopt as the criterion of " youth " 
a condition which has no sure place in the ideal normal history 
of shoreline development. 

The three considerations set forth above force us to the con- 
clusion that no great profit is to be derived from the attempt to 
distinguish different stages of shoreline development according 



PROGRESSIVE SUBSIDENCE ON LAGOON HISTORY 383 

to whether the offshore bar is prograding or retrograding, whereas 
considerable confusion and misunderstanding is apt to result 
from such an attempt. We will therefore regard the offshore 
bar, with its associated lagoon or marsh, as characteristic of 
the youthful stage of the shoreline of emergence, making no 
attempt, in the present state of our knowledge of shorelines, to 
further subdivide the stage of youth. On this basis the New 
Jersey shoreline, from Bay head to Cape May City, is a young 
shoreline of emergence. 

Cuspate Offshore Bars. — Occasionally an offshore bar has a 
pronounced cuspate pattern. Such is the case at the Carolina 
Capes, on the offshore bar bordering North Carolina. Like 
ordinary cuspate bars, the cuspate form of offshore bars may 
be produced in a variety of ways. A favorite theory is that 
proposed by Abbe 27 for the Carolina Capes, and supported by 
Gulliver 28 and Davis 29 according to which the cusps result from 
deposition in the triangle of quieter water between two adjacent 
circling currents. A shoal or a former island some distance off 
a straight coast not infrequently produces a cuspate pattern in 
adjacent parts of an offshore bar. If the initial shoreline of 
emergence has pronounced projections or capes, then the off- 
shore bar which is parallel to that shoreline will of necessity 
have a cuspate form imposed upon it. A study of the inner 
shoreline, back of the Carolina offshore bars, shows that the 
mainland itself possessed initial capes, later more or less cut 
back by wave action, which are perhaps fully competent to 
explain the Carolina cuspate bars. 

Effect of Progressive Subsidence on Lagoon History. — If a 
shoreline of emergence bordered by an offshore bar is subjected 
to a gradual but continuous subsidence, certain departures from 
the normal history outlined above may be noted. Subsidence 
tendc to deepen the water in front of the bar, thus enabling 
larger and more powerful waves to attack its face. This must 
result in an abnormally rapid retreat of the bar, since a bar 
moves landward just as fast as the water in front of it is deep- 
ened sufficiently to permit the near approach of large waves, 
whatever be the cause of deepening.. If to the deepening per- 
formed by normal wave erosion we add a deepening due to 
progressive subsidence, certainly the landward movement of 
the bar will be appreciably accelerated. This does not mean 



384 



DEVELOPMENT OF THE SHORELINE 



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PROGRESSIVE SUBSIDENCE ON LAGOON HISTORY 385 

that the lagoon or marsh will be correspondingly narrowed, 
since subsidence causes the inner shoreline to encroach upon 
the land at the same time, and presumably at about the same 
rate that the bar moves landward. Both the bar and its asso- 
ciated lagoon or marsh advance upon the coast simultaneously. 
Migrating inlets, tidal deltas, and other shore phenomena de- 
velop as before. Sedimentation proceeds in the lagoon, but is 
not so apt to fill it as when the coast is stationary, since subsi- 
dence carries the bottom deposits downward and continually 
renews the water space which must be filled. 

When a marsh has formed back of the bar, later subsidence, if 
not too rapid, may bring about several peculiar results. In the first 
place, as the surface of the marsh with its high-tide grasses is 
carried downward, new growths of grass continually arise upon 
the old in an effort to keep the marsh built up to the high- tide level 
(Plate XLV) . The importance of this process was first recognized 
by Mudge 30 more than half a century ago, and has 1-ater been 
much emphasized by C. A. Davis 31 . The result is a deposit of 
salt marsh peat, composed of the roots and other remains of 
high-tide grasses, whose depth is an approximate measure of the 
minimum amount of subsidence. Sections through such a salt 
marsh, instead of showing high-tide grasses above, remains of 
eel-grass and other low-level grasses immediately below, and 
nearly pure silt or clay throughout the remaining depth of the 
lagoon deposit, as we should expect according to the Shaler 
theory of salt marsh formation, might show nothing but remains 
of high-tide vegetation from top to bottom, providing subsidence 
had progressed far enough to allow the offshore bar to move 
landward past the former position of the inner shoreline, and 
hence beyond the farthest limit of the initial lagoon deposits. 
As the salt marsh is progressively built upward it gradually en- 
croaches upon the gently sloping surface of the subsiding main- 
land, overwhelming and burying the fresh-water vegetation 
which clothes that surface. Remains of the land vegetation may 
thus be preserved as a layer of fresh-water peat at the bottom 
of the salt marsh deposit, and may later be encountered in sec- 
tions cut through the marsh to the solid ground below. 

Another consequence of gradual subsidence after the marsh 
has formed is the complete disappearance of the nip along the 
margin of the mainland. So long as the lagoon persists, the 



386 DEVELOPMENT OF THE SHORELINE 

lagoon waters encroaching upon the subsiding mainland may be 
sufficiently agitated by winds to cut a small cliff at whatever 
level the water may stand. But after the marsh has once filled 
the lagoon area, there remains no force capable of cutting a 
straight cliff along the mainland shore, while the former wave- 
cut nip is carried downward under the marsh by subsidence and 
so lost to view. Thereafter the marsh surface and the gently 
sloping mainland surface intersect at a low angle which is often 
almost imperceptible. 

Effect of Progressive Elevation on Lagoon History. — A 
gradual uplift of the sea-bottom, by decreasing the depth of 
water in front of the offshore bar, tends to cause the waves to 
break farther and farther seaward. If the elevation is so very 
slow that the normal tendency of the waves to deepen the water 
in front of the bar by erosion is not completely counteracted, 
the bar will retreat as on a stable coast, but more slowly. Should 
elevation just balance deepening by wave erosion, we should 
expect the bar to remain approximately in its original position 
while its crest was raised higher and higher out of the water and 
the lagoon became dry through emergence. Were elevation 
slightly more rapid, the waves would prograde the bar by 
adding successive ridges to its face as they broke farther and 
farther seaward. The older ridges would normally have a higher 
average crest elevation, through uplift, than would the later 
and hence less uplifted members of the series. The lagoon or 
marsh would disappear or dry up as the depression it occupied 
was raised above sealevel. Very rapid elevation might pre- 
vent the formation of well-developed ridges in front of the 
original bar; or if the rapid elevation began before any bar 
had formed, the bar and lagoon might not come into exist- 
ence at all until elevation had ceased or become much more 
gradual. 

Offshore Bars not an Evidence of Subsidence. — On an 
earlier page we have referred to the fact that certain authors 
are inclined to regard offshore bars as an evidence of coastal 
subsidence. We are now in a position to return to this theory, 
and consider it in the light of our discussion of the normal his- 
tory of the offshore bar. It should be noted in the first place 
that in so far as the subsidence theory of bar formation has 
been elucidated by its supporters, it would seem to rest upon 



OFFSHORE BARS NOT AN EVIDENCE OF SUBSIDENCE 387 

one or the other of two misapprehensions regarding the history 
of offshore bars. McGee 32 and Ganong 33 assume that waves 
must begin to build up deposits of sand and gravel immediately 
at the margin of the original coast. Offshore bars must there- 
fore represent former coast-margin beaches which have been 
built vertically upward as the land subsided and the receding 
shoreline moved inland. The assumption upon which the argu- 
ments of McGee and Ganong depend for their validity is, how- 
ever, directly opposed to the conclusions of practically all stu- 
dents of shoreline phenomena, to theoretical considerations based 
on the principles of shoreline development as outlined above, and 
to observed facts. 

It is not necessarily a serious objection to any theory to say 
that it is opposed to the conclusions of former investigators. 
Theoretical considerations, however, are directly in conflict with 
the assumption that offshore bars must have begun as ordinary 
shore beaches at the margin of the mainland. In our elabora- 
tion of the theory of shoreline development we have seen that 
the laws of wave action, according to which waves break in a 
depth of water about equal to the wave height, require a zone 
of breakers some distance from the mainland on a gently sloping 
shore. If waves breaking at the mainland margin erode the 
bottom and cast up part of the debris to form a beach ridge, 
we should expect larger waves breaking offshore to erode the 
bottom and cast up part of the debris to form an offshore ridge 
or bar. Moreover, according to the theory of wave action, 
subsidence, by deepening the water in front of the wave-built 
deposit, enables larger waves to attack the deposit in the effort 
to drive it landward. If waves could reach the mainland 
shore to build a beach deposit before subsidence began, it is 
difficult to see why more intense wave action under the more 
favorable conditions induced by subsidence should be unable 
to keep the deposit pushed back to the same relative position 
as the shoreline receded. The fact that the best development 
of offshore bars is found where geologically recent uplift has 
brought a smooth, gently sloping sea-bottom within the zone 
of effective wave action, is in accord with what we should expect 
if the theoretical considerations elaborated on preceding pages 
are correct; whereas the absence or poor development of such 
bars on many coasts known to have suffered subsidence in geo- 



388 DEVELOPMENT OF THE SHORELINE 

logically recent times is distinctly unfavorable to the theory 
which attributes such bars to subsidence. 

Recorded observations prove that bars may be produced by 
waves breaking some distance out from the main shoreline. 
We have historical evidence of a few cases of this kind on a 
large scale, such as the Yarmouth bar on the east coast of Eng- 
land; on a smaller scale the process may be observed along 
the shallow shores of lakes and ponds. The writer has seen a 
very perfect miniature offshore bar formed in a few hours by 
waves raised on the surface of a small lake at Lakehurst, New 
Jersey, during a fresh breeze. The bar was a few inches in 
width, and separated a shallow lagoon one or two feet broad 
from the gently sloping sandy shore which it paralleled for 
some yards. 

It is possible to read another meaning into the words used 
by McGee; and as this alternate interpretation may be held 
by others who regard offshore bars as proofs of subsidence, we 
will briefly consider it. In citing offshore bars (which he calls 
" keys ") as an evidence of coastal depression, McGee uses the 
phrase: " the rapidly-encroaching sea having outstripped the 
slow-moving keys and left them far behind 34 ." We might con- 
ceive this to mean that while the offshore bar was first formed 
by storm waves some distance out from the mainland shore, 
and possibly began to retreat landward under normal wave 
attack, subsidence intervened at so rapid a rate that the inner 
shoreline encroached upon the land faster than the bar could 
follow. Hence, one might argue, there is still a great breadth of 
lagoon or marsh between the bar and the mainland, whereas 
there would have been none by this time had it not been for 
subsidence. 

The validity of this argument must depend upon two assump- 
tions: first, that we know how long it normally takes a bar to 
move from its initial position to the mainland when not affected 
by subsidence; and second, that the bar was built that long 
ago. Neither of these assumptions is supported by any evi- 
dence thus far brought to light. We do not know the length 
of time required for an offshore bar on a stable coast to retreat 
to the mainland, nor do we know how long ago the bars on the 
New Jersey and other parts of our coast were formed We 
are not justified, therefore, in assuming that the persistence to 



MATURE STAGE 389 

the present day of a lagoon or marsh back of the bar is in any 
wise related to coastal subsidence., 

Mature Stage. — The offshore bar is a temporary feature, 
built by the waves because the initial slope of the upraised sea- 
bottom was not in harmony with the marine forces operating 
upon it. Once the bar is fully developed, and the steeper 
slope of its seaward side is brought into approximate adjust- 
ment with the waves which break against it, the normal retreat 
of the shoreline may begin. Constant loss of the finer products 
of attrition, which are swept into deep water by current action, 
enables the waves to drive the bar slowly landward. Tempo- 
rary prograding may interrupt the retreat from time to time, 
as already explained; but such interruptions can have no effect 
on the ultimate history of the bar. It is inevitably forced farther 
and farther up the gentle slope of the lagoon bottom, or across 
the surface of the marsh deposits, toward the initial shoreline. 
The advancing waves cut farther and farther into the original 
sea-bottom in order to preserve the same depth of water imme- 
diately in front of the retreating bar. A time must come when 
the bar has been forced clear back upon the mainland, the lagoon 
or marsh has been wholly destroyed, and the steeper slope to 
deep water required by large storm waves lies just at the edge 
of the land. The shoreline of emergence is then said to be 
mature (stage H, Fig. 119). 

Just as in the case of the shoreline of submergence, maturity 
of the shoreline of emergence is characterized by a very simple 
pattern. Indeed, it is apt to be much more nearly straight for 
long distances than is the mature shoreline of submergence, 
since it develops from a young shoreline which was itself straight 
or of simple curvature. The marine cliff bordering the shore 
may be very low and insignificant in early maturity, but will 
increase in altitude as the waves cut farther into the sloping 
coastal plain. When wave attack is vigorous the cliffs may 
themselves be young. This is especially apt to be the case 
during the early maturity of the shoreline. A narrow beach 
may intervene between the base of the cliff and the water; 
but owing to the changing profile of equilibrium under varying 
conditions of wave attack, the beach deposit may be tempo- 
rarily removed and the bare rocky surface of the marine bench 
exposed for a time. In height the cliff will normally be more 



390 DEVELOPMENT OF THE SHORELINE 

uniform than that bordering a mature shoreline of submergence, 
since it is carved in the margin of a plain formed by the com- 
paratively smooth uplifted sea bottom. The cliff line will be 
interrupted by the valleys of those main streams which are 
sufficiently active to cut their channels down to sealevel as 
rapidly as the waves push the shoreline inland. Smaller and 
weaker streams may descend from hanging valleys opening well 
up on the face of the cliff, the height of the valley mouth above 
sealevel being a measure of the relative incompetency of the 
stream which occupies it. 

It is hardly probable that an offshore bar would retreat at 
such rate in all its parts as to reach the mainland shore simul- 
taneously throughout its entire length. We must rather expect 
that a stage will occur when many parts of the bar touch the 
mainland, while along other parts narrow remnants of the lagoon 
still intervene between bar and inner shoreline. Especially will 
this be the case where the mainland shore was mildly irregular 
in outline. We may speak of such a shoreline as in the sub- 
mature stage of its development, and cite the shore of the Landes 
district of southwestern France as an example. The cliffs at 
Long Branch on the New Jersey coast may be regarded as 
bordering a mature shoreline of emergence. 

One effect of shoreline retrogression upon the drainage pat- 
tern of a coastal plain demands a word in this connection. 
Abbe 35 has described the asymmetrical position of the divides 
along the shores of Chesapeake Bay and its branches, where 
the water parting lies nearest to the shore which is retreating 
most rapidly. This is due in part, at least, to the fact that 
wave erosion cuts off the lower ends of the valleys faster than 
headward stream erosion can push the divide back to a position 
of stable equilibrium. The divide tends to migrate away from 
that shore which is retrograding most rapidly; but its migration 
is sluggish as compared with the rate at which the waves push 
the shoreline toward the divide. Hence the unsymmetrical 
position of the latter. 

Old Stage. — There are striking differences between a young 
stream and a mature . stream ; but no such marked contrast 
exists between mature and old streams. Similarly, while the 
contrasts between young and mature shorelines are sufficiently 
remarkable to call for much comment, whether in the case of 



OLD STAGE 391 

shorelines of submergence or shorelines of emergence, little that 
is new can be said regarding old shorelines of either class. The 
remarkable lack of adjustment between shoreline and shore 
processes which characterizes the stage of youth, is replaced 
by a nearly perfect adjustment in maturity; and this same 
adjustment continues throughout old age. In like manner the 
relatively simple shoreline of maturity, bordered on the one 
side by a sufficient depth of water for wave action close to the 
land, and on the other by marine cliffs, persists into the latest 
stage of shoreline development. The water depth immediately 
adjacent to the shoreline may decrease as the marine bench is 
broadened and the movement of waves across it is retarded in 
old age; the cliff may weather back to a more gentle slope than 
it possessed during maturity, and hanging valleys may disappear 
as smaller streams become able to keep pace with the slower re- 
treat of the shoreline. But such changes are of moderate impor- 
tance as compared with the remarkable transformation which 
takes place between youth and maturity of the shoreline cycle. 

It must not be forgotten, however, that the old age of a 
shoreline is largely a matter of theory. No good example of a 
shoreline in this stage of development is known to exist at the 
present time. Young and mature shorelines are well known; 
and from them we may reasonably infer what some of the char- 
acteristics of old age must be. On the other hand there are 
some questions concerning which we must speak with more 
reserve. Thus we have seen that as a land mass approaches 
the condition of peneplanation, the rivers can bring out very 
little debris, and waves will accordingly have less river-brought 
material to deal with. Under these conditions they may be 
able to attack more vigorously the task of eroding the coast 
and removing the wave-formed debris. How will the rate of 
shoreline retrogression then compare with the earlier rate? 
How will the depth of water near the shoreline, the slope of the 
marine cliff, and the condition of hanging valleys then compare 
with similar features at an earlier stage of the shoreline cycle? 
We might discuss such questions at length from the theoretical 
standpoint; but it would be difficult to confirm our theoretical 
conclusions by confronting them with facts observed in the 
field. Such consideration of these problems as appears to be 
profitable has already been given in Chapter V. 



392 DEVELOPMENT OF THE SHORELINE 

RESUME 

In the present chapter we have traced the development of the 
shoreline of emergence from the initial stage through its youth 
and maturity to old age. We have paused long enough to dis- 
cuss at some length the origin of offshore bars, and have con- 
cluded that they are constructed for the most part of material 
eroded from the sea-bottom by onshore wave action, as was early 
stated by de Beaumont; although the action of longshore cur- 
rents upon which Gilbert relied plays a significant role in their 
later history. It has been shown that the theory of tidal inlets 
which would explain their frequency and breadth as due to the 
amplitude of the tidal range, is in itself inadequate; and that the 
distribution of inlets, the breadth of lagoons, and the amount of 
lagoon filling are determined in part by the extent to which 
debris is transported along the face of the offshore bar by long- 
shore current action. A study of migrating inlets has developed 
the important conclusion that an offshore bar broken by such 
inlets may exhibit the same cross section after migrating far 
landward over a salt marsh deposit as it did in its initial stage. 
We have given special attention to the effects of subsidence and 
elevation upon offshore bars, lagoons, and marshes; and have 
found that there is no support for the conception that offshore 
bars are an indication of coastal subsidence. 

REFERENCES 

1. Bryson, John. [On the beaches along the southern side of Long Island.] 

Amer. Geol. II, 64, 1888. 

2. Bryson, John. The so-called Sand Dunes of East Hampton, L. I. 

Amer. Geol. VIII, 188, 1891. 

3. Schott, Arthur. Die Kiistenbildung des Nordlichen Yukatan. Pet. 

Geog. Mitt. XII, 127-130, 1866. 

4. Agassiz, Louis. On the Relation of Geological and Zoological Researches 

to General Interests, in the Development of Coast Features. U. S. 
Coast Survey, Rept. for 1867, p. 184, 1869. 

5. Merrill, F. J. H. Barrier Beaches of the Atlantic Coast. Popular 

Science Monthly. XXXVII, 744, 1890. 

6. McGee, W. J. Encroachments of the Sea. Forum, IX, 443, 1890. 

7. Ganong, W. F. Notes on the Natural History and Physiography of 

New Brunswick, N. B. Nat. Hist. Soc, Bull., No. XXVI, Vol. VI, 
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8. Goldthwait, J. W. Supposed Evidences of Subsidence of the Coast 

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REFERENCES 393 

9. Beaumont, Elie, de. Lecons de Geologie Pratique, pp. 223-252, Paris, 
1845. 

10. Shaler, N. S. Beaches and Tidal Marshes of the Atlantic Coast 

National Geogr. Monogr. I, 151-153, 1895. 

11. Gilbert, G. K. The Topographic Features of Lake Shores. U. S. 

Geol. Surv., 5th Ann. Rep., p. 87, 1885. 
Gilbert, G. K. Lake Bonneville. U. S. Geol. Surv. Mon. I, 40, 1890. 

12. Russell, I. C. Geological History of Lake Lahontan. U. S. Geol. 

Surv. Mon. XI, 90, 1885. 

13. Gilbert, G. K. Lake Bonneville. U. S. Geol. Surv. Mon. 1,43-45, 

1890. 

14. Ibid., p. 97 and Plate XX. 

15. Russell, I. C. Geological History of Lake Lahontan. U. S. Geol. 

Surv. Mon. XI, 90, 1885. 

16. Gilbert, G. K. Lake Bonneville. U. S. Geol. Surv. Mon. I, 40, 1890. 

17. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

p. 710, Boston, 1909. 

18. Davis, W. M. Die Erklarende Beschreibung der Landformen, pp. 

471-473, Leipzig and Berlin, 1912. 

19. Shaler, N. S. Beaches and Tidal Marshes of the Atlantic Coast. Na- 

tional Geogr. Monogr. I, 153, 1895. 

20. Weidemuller, C. R. Die Schwemmlandkusten der Vereinigten Staaten 

von Nordamerika, p. 29, Leipzig, 1894. 

21. Davis, W. M. Physical Geography, p. 353, Boston, 1898. 

22. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 179, 1899. 

23. Davis, W. M. Die Erklarende Beschreibung der Landformen. Fig. 

188, Leipzig and Berlin, 1912. 

24. Shaler, N. S. Preliminary Report on Sea-coast Swamps of the Eastern 

United States. U. S. Geol. Surv., 6th Ann. Rept., p. 364, 1886. 

25. Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad. Arts and 

Sciences. XXXIV, 183-185, 1899. 

26. Davis, W. M. Die Erklarende Beschreibung der Landformen, p. 478, 
02 Leipzig and Berlin, 1912. 

27. Abbe, Cleveland, Jr. Remarks on the Cuspate Capes of the Carolina 

Coast. Proc. Bost. Soc. Nat. Hist. XXVI, 496, 1895. 

28. Gulliver, F. P. Cuspate Forelands. Bull. Geol. Soc. Amer. VII, 

407-410, 1896. 

29. Davis, W. M. Die Erklarende Beschreibung der Landformen, pp. 

478-477, Leipzig and Berlin, 1912. 

30. Mudge, B. F. Salt Marsh Formation of Lynn. Essex Institute Proc. 

II, 117-119, 1862. 

31. Davis, Chas. A. Salt Marsh Formation near Boston and its Geological 

Significance. Economic Geology, V, 623-639, 1910. 
Davis, Chas. A. Some Evidences of Recent Subsidence on the New 

England Coast. Science New Ser., XXXII, 63, 1910. 
Davis, Chas. A. Salt Marshes, a Study in Correlation. Assoc. Am. 

Geographers, Annals. I, 139-143, 1911. 



394 DEVELOPMENT OF THE SHORELINE 

32. McGee, W. J. Encroachments of the Sea. Forum, IX, 443, 1890. 

33. Ganong, W. F. Notes on the Natural History and Physiography of 

New Brunswick, N. B. Nat. Hist. Soc, Bull. No. XXVI, Vol. VI, 
pt. I, p. 21, 1908. 

34. McGee, W. J. Encroachments of the Sea. Forum, IX, 443, 1890. 

35. Abbe, Cleveland. A General Report on the Physiography of Mary- 

land. Maryland Weather Service. I, 104, 1899. 



CHAPTER VIII 

DEVELOPMENT OF THE SHORELINE (Continued) 

C. NEUTRAL AND COMPOUND SHORELINES 

Neutral Shorelines. — It would not be appropriate in the 
present volume to discuss at length the developmental history of 
all the different types of neutral shorelines. The general princi- 
ples outlined under the preceding discussion of shorelines of sub- 
mergence and shorelines of emergence present a foundation upon 
which the student may base a treatment of any neutral shore- 
line, making such minor modification of treatment as the special 
peculiarities of the particular type may warrant. We may note 
in passing, however, that alluvial plain and outwash plain shore- 
lines, like the shoreline of the coastal plain, have a simple pat- 
tern in the initial as well as in later stages; but that unlike the 
latter type, they need not pass through an offshore bar stage 
because of their steeper seaward slope from the water margin. 
Lobate delta shorelines pass through a submature stage in which 
an arcuate pattern is given to the outer shoreline by the build- 
ing of bars connecting the seaward extremities of the lobes. 
Portions of the Rhone and Nile deltas appear to possess shore- 
lines representing this stage of development. A true arcuate 
delta shoreline may characterize the mature stage of a lobate 
delta shoreline, if wave erosion cuts back the lobes beyond the 
heads of the inter-lobe bays (Fig. 120). An appreciation of the 
variety of delta types responsible for some of the variations in 
delta shorelines may be gained from an inspection of Credner's 
well-known essay on " Die Deltas 1 ". 

A valuable discussion of delta formation is given by Barrell in an 
essay on " Criteria for the Recognition of Ancient Delta Deposits." 
The " delta cycle" is thus briefly summarized by this author: 
" In the stage of youth before the drainage system has become 
well developed the detritus delivered at the river mouth is some- 
what smaller in amount but coarser in texture. The subaqueous 
wave-cut profile is also undeveloped, the bottom still inheriting 

395 



396 



DEVELOPMENT OF THE SHORELINE 



its original slope. If this initial slope is gentler than the sub- 
aqueous profile of equilibrium the waves have at first less power 
of erosion at the coast line. If the initial slope is steeper they 
will possess an initially greater power. Assuming, however, 
that the river is dominant over the sea, the delta is rapidly 




Fig. 120. — Diagram showing how wave erosion of a lobate delta may trans- 
form it into an arcuate delta (broken line). 

built outward, and on account of the coarse waste, the steeper 
river grades, and shallow bottom near shore, the initial propor- 
tion of the subaerial topset beds is relatively high. During 
maturity the quantity of waste is larger, as all parts of the 
drainage system now supply sediment, but as the river is graded 
and its gradient is also flattened the waste is finer in texture. 
The delta is extended outward and the greater deposit is on the 
outer portions. It grows inland also for a time, but owing to 
the flattening grade the beds in this direction show decreasing 
thickness. The maximum rate of outward growth is reached 
early because of the increasing surface area, which requires a 
greater volume of sediment to give a unit thickness, and the 
increasing depth of the water, which involves a continually 
deeper fill. Furthermore, the increasing shoreline and greater 
exposure to the waves increase the power of the latter to carry 
away the waste, which with the progress of the cycle becomes 
finer in texture and more readily removed by the sea. But 
although the rate of advance falls off, the outward growth will 
continue during the progress of maturity in the cycle of erosion 
and deposition. In old age, however, on account of the ever- 
slackening supply of waste and the larger portion carried in 



NEUTRAL SHORELINES 



397 



suspension and solution, the sea at last gains the mastery and 
begins to plane inland across the low-lying and unconsolidated 
materials projecting into the sea. Rapid headway is finally 
made against the weakened river; the territory conquered by 
the river in its youth is reclaimed and the sea at last will beat 
once more against the margin of the old land 2 ". 

The development of fault shorelines has been ably discussed 
by Cotton 3 , who presents a detailed analysis of the features 




Fig. 121. — Fault shoreline bordering a scarp which dies out toward the 
right. The fault traversed a region of strong relief. (Modified after 
Cotton.) 

characterizing successive stages in the life history of such shore- 
lines. As he is careful to point out, the initial character of the 
fault shoreline will vary widely according as the fault traverses 
a maturely dissected land mass of strong relief (Fig. 121), or an 
undissected coastal plain of no appreciable relief (Fig. 122). 
In either case streams betrunked by faulting will cascade into 
the sea from the mouths of hanging valleys. Thus the initial 
stage of fault shorelines resembles the mature stage of shore- 
lines of submergence in cases where the relatively simple cliff- 
line of the latter type is marked by hanging valleys due to 



398 DEVELOPMENT OF THE SHORELINE 

rapid wave attack. The character of the seaward slope, how- 
ever, is very different in the two cases. Where the landward 
block bordering a fault shoreline has itself been partially de- 
pressed, thereby bringing the main valley floors at the fault 
scarp down to sealevel, there will be no large hanging valleys. 




Fig. 122. — Similar to Fig. 121, except that the fault traversed a little- 
dissected plain of faint relief. (Modified after Cotton.) 

If the landward block has been depressed sufficiently to permit 
the sea to enter and submerge the main valleys, we have an 
initial compound shoreline (Fig. 124), the treatment of which 
type is reserved for a later section. Seaward from the fault 
scarp the sea floor will have the contours of the pre-faulting land 
surface, whether that be an irregular surface (Fig. 121) or a 
smooth plain (Fig. 122). The seaward slope in the immediate 
vicinity of the shoreline will normally be very steep, as it is the 
slope of the fault scarp itself. 

Wave attack on the fault scarp will not proceed very rapidly 
at first, both because steep walls rising out of deep water 
tend to reflect waves, and because the waves are unarmed with 
rock fragments with which to make their attack more effective. 
The face of the cliff will weather back to a more moderate slope, 
and the weathering products will accumulate at the cliff base as 
a subaqueous talus. Streams emptying from hanging valleys will 
rapidly entrench themselves, cutting young gorges in the more 
mature valleys of the initial land surface, thus producing a 



NEUTRAL SHORELINES 399 

typical two-cycle topography without necessarily implying any 
change in the level of the land area in question or of the adjacent 
water surface. The erosion products brought out by the streams 
will accumulate as subaqueous talus cones which may later 
take the form of ordinary deltas. With the shallowing of the 
bottom near shore by accumulations of debris derived from 
fault face and stream valleys, wave reflection is less perfect 
and wave attack more vigorous, particularly since supplies of 




Fig-. 123. — Successive stages in the retrogression of a fault shoreline 
bordering rocks of varying resistance. 

rock fragments are now accessible to the waves. The retreat 
of the shoreline takes place more rapidly for a time. Later, 
when the marine bench and shoreface terrace have attained a 
considerable width, the vigor of the waves traversing them is 
somewhat reduced for reasons explained on earlier pages; and 
the marine cliff, steepened while wave attack was increasing in 
vigor, has opportunity to weather back to a more gentle slope. 
The fault shoreline has now reached maturity, and henceforth 
develops in the same manner as other mature shorelines. As 
noted under shorelines of submergence, a shoreline bordering 



400 DEVELOPMENT OF THE SHORELINE 

weak rock areas will retreat more rapidly than one bordering 
regions of resistant rock. From this it follows that an initially 
straight fault shoreline may acquire a pattern of simple curves 
in maturity, the re-entrant curves being systematically related 
to weak rock areas (Fig. 123). 

Compound Shorelines. — Thus far we have considered the 
developmental stages of shorelines of submergence, shorelines of 
emergence, and neutral shorelines. It remains only to point out 
very briefly any special features characteristic of different stages 
of compound shorelines, or those shorelines which exhibit promi- 
nently features normally characteristic of at least two of the 
foregoing classes. 

In its young stage a compound shoreline combining features 
of both submergence and emergence will be characterized by 
an offshore bar which determines a straight outer shoreline, and 
drowned valleys which give an irregular inner shoreline. The 
bar may be broken by tidal inlets and possess all the other fea- 
tures of such a bar on a shoreline of emergence. Similarly, the 
lagoon may in course of time become filled with sediment or 
marsh deposits. Whether or not such filling occurs, the various 
types of spits, forelands, and bars which are so marked a feature 
of young and submature shorelines of submergence, are largely 
lacking along the irregular inner part of the compound shore- 
line, for the reason that the offshore bar protects the inner shore 
from the effective wave action which is, as we have already 
seen, largely responsible for these shore forms. 

Such a compound shoreline may be called submature when 
the offshore bar has been driven against the headlands of the 
inner shore. The bays between the headlands will then appear 
to be closed by bay bars; and cases may occur in which a sub- 
mature compound shoreline could not be distinguished from a 
submature shoreline of submergence. In the latter type of shore- 
line, however, the bars closing the different bays have devel- 
oped more or less independently; and it is doubtful whether 
they will ordinarily show that relatively straight alignment char- 
acteristic of the different parts of a single offshore bar which has 
been driven against the headlands of the irregular inner part of 
a compound shoreline. Maturity is reached when outer and 
inner shoreline have coalesced in one shoreline back of the heads 
of the initial embayments. From this time on the features of 



CONTRAPOSED SHORELINES 401 

the compound shoreline do not differ from those of the shoreline 
of emergence. 

A compound shoreline combining features of a fault shore- 
line with those of a shoreline of submergence (Fig. 124) passes 
through a first stage in which the outer or fault shoreline por- 
tion develops like any normal fault shoreline, while the drowned 
valley portions of the partially submerged block have the same 
history as the more deeply indented portions of normal shore- 



UiG. 124. — Compound shoreline, combining essential features of a shore- 
line of submergence and a fault shoreline. 

line of submergence. Maturity is reached when wave erosion 
has pushed the initial fault scarp, later become a normal marine 
cliff, back of the bay heads, and a simple shoreline bordered by 
a continuous marine cliff is developed. Further stages of de- 
velopment show no peculiar features. 

Contraposed Shorelines. — If a coastal region of hard rocks is 
separated from the sea by a belt of overlapping softer deposits, 
as where a rugged oldland is overlapped by a narrow coastal 
plain, the shoreline which is first developed upon the softer beds 
will later be retrograded until it comes against the hard rocks. 
Such a shoreline has well been called " contraposed V by C. H. 
Clapp 4 , and in origin it is analogous to a " superposed " river 
which has been let down from a soft rock cover upon under- 
lying ridges of harder material. A shoreline which has reached 
maturity in the softer beds may in its contraposed position lose 



402 



DEVELOPMENT OF THE SHORELINE 










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its mature characteristics and acquire those of youth (Fig. 125). 
It may even change from a typical shoreline of emergence to one 
having the characteristics of submergence, if the older and 




Fig. 125. — Stages in the formation of a contraposed shoreline. Early 
stage shown by upper figure. (Modified after Clapp.) 

harder rocks possessed a very rugged surface and the soft rock 
mantle consisted of unconsolidated material easily removed. 
Parts of the New England shoreline belong to the contraposed 
type (Plate XL VI). 

REFERENCES 

1. Credner, G. R. Die Deltas. Pet. Geog. Mitt., Erganzungsband XII, 

No. 56, 1-74, 1878. 

2. Barrell, Joseph. Criteria for the Recognition of Ancient Delta De- 

posits. Bull. Amer. Geol. Soc. XXIII, 397, 1912. 

3. Cotton, C. A. Fault Coasts in New Zealand. The Geographical Re- 

view. I, 20-47, 1916. 

4. Clapp, C. H. Contraposed Shorelines. Jour, of Geol. XXI, 537, 1913, 






CHAPTER IX 
SHORE RIDGES AND THEIR SIGNIFICANCE 

Advance Summary. — Many beaches, bars, tombolos and fore- 
lands are characterized by a succession of narrow ridges built by 
the waves, and sometimes later modified by the winds. These 
" lines of growth" of shore forms have much significance for the 
engineer who would learn something of current action and direc- 
tion of debris movement at a given locality in the recent past, 
and for the geological or geographical student who would trace 
the development of shore forms and ascertain what light they 
may throw upon the important question of past changes in the 
relative levels of land and sea. It is the purpose of the present 
chapter to discuss the origin of beach ridges and dune ridges; to 
inquire into the rate at which they have been formed, with the 
hope of acquiring data useful in estimating the ages of those 
shore forms which possess them; and, finally, to analyze in a 
critical manner the conditions under which beach ridges may be 
used to determine whether coasts have recently experienced appre- 
ciable changes of level. 

Origin of Beach Ridges. — Beach ridges have long been 
recognized as representing successive positions of an advancing 
shoreline, and are known to the English as " fulls"; while the 
depressions between them are known as " swales," " slashes," 
or " furrows." When a beach ridge is covered by dune sands 
we have a "dune ridge"; the swales between dune ridges have 
been called " dune valleys " (Diinentaler) by the Germans. Un- 
usually good examples of beach ridges or dune ridges are found 
on Orford Ness on the east coast of England as described by 
Redman 1 ; on the Dungeness foreland of the southeast coast, 
described by Drew 2 , Redman 3 , and Gulliver 4 ; on the Darss fore- 
land of the Baltic coast of Germany described by Otto 5 in a 
paper on " Der Darss and Zingst "; at Swinemiinde on the same 
coast where a most remarkable series of dune ridges has been 
described by Keilhack 6 in a most interesting essay entitled " Die 

404 



ORIGIN OF BEACH RIDGES 405 

Verlandung der Swinepf orte " ; and on Cape Canaveral off the 
east coast of Florida. ' Beach or dune ridges are usually found in 
a greater or less degree of perfection on any prograded shoreline, 
and they are of so much importance, not only in showing the 
successive stages of development of the forms which possess them, 
but also, as will presently appear, in showing whether a coast 
has remained stable or experienced changes of level during their 
formation, that it is pertinent to inquire somewhat fully into 
their origin and significance. 

According to Gilbert 7 a wave-built terrace or beach plain is 
usually produced whenever a shoreline maintains its course 
while the longshore current diverges. " The surface of the 
wave-built terrace, considered as a whole, is level, but in detail 
it is uneven, consisting of parallel ridges, usually curved. Each 
of these is referable to some exceptional storm, the waves of 
which threw the shore drift to an unusual height 8 ". The 
forward building of the shore occurs because the diverging 
current assumes a greater cross section and a diminished veloc- 
ity; and with diminished velocity an accumulation of the trans- 
ported debris must take place. " This accumulation occurs, 
not at the end of the beach, but on its face, carrying its entire 
profile lakeward and producing by the expansion of its crest a 
tract of new-made land." i 

Davis 9 explains the prograding of an offshore bar by suppos- 
ing that waves breaking on a shallowing sea floor cast up the 
bottom material into an initial bar or ridge; later, larger storm 
waves break a little farther out in deeper water, and from the 
newly eroded bottom material construct another bar on the 
face of the earlier one. " A preliminary offshore bar is built 
up by the storm waves . . . ; and afterwards, at times of 
exceptional storms, successive additions may be made on its 
outer side 10 ."< According to this theory, also, the accumulation 
occurs on the face and not on the end of the earlier deposit; but 
the material is supposed to be derived from the sea-bottom and 
not from the longshore currents upon which Gilbert relied. 

When a recurved spit develops into a compound spit or fore- 
land by the addition of successive spits or embankments to its 
seaward side, there is produced a beach plain characterized by 
sub-parallel ridges separated by belts of lower land or strips of 
water. In this case, however, the accumulation may take place 



406 



SHORE RIDGES AND THEIR SIGNIFICANCE 




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ORIGIN OF BEACH RIDGES 407 

not simultaneously along the entire face of the earlier deposit, 
but by extension of the ends of the successively formed embank- 
ments; longshore currents furnish the principal supply of mate- 
rial; and the individual ridges are evidently not to be correlated 
with a corresponding number of great storms. Davis 11 appears 
to regard the beach ridges of the Provincelands as having been 
produced in the manner here indicated, although his admirable 
essay on " The Outline of Cape Cod" does not explicitly state 
that the successive embankments all grew longitudinally from 
their point of tangency with the mainland cliff. 

It is highly probable that ridged beach plains have been 
produced in all three of the ways mentioned above. Where 
one part of a shore is being cut back and straightened by the 
waves, a longshore current may have its course so modified as 
to depart from an adjacent section of the shore which it pre- 
viously followed. If the withdrawal is gradual enough, the 
portion of the shore affected may continuously be prograded by 
deposits laid down in the manner described by Gilbert. Where 
the withdrawal is more rapid, successive separate embank- 
ments may build a compound spit or foreland bar. Interme- 
diate forms between these two types must exist. Sandy Hook 
in its earlier development appears to have consisted of several 
embankments built independently from southeast to northwest, 
one after the other;, but in later years it seems possible that its 
whole seaward face has advanced eastward at times by practi- 
cally simultaneous deposition along its length. There is likewise 
good reason to believe that some offshore bars have been slightly 
prograded by the building of one or more embankments in the 
deeper water outside of the original bar, after the manner sug- 
gested by Davis. In the opinion of the present writer, however, 
the processes described above are not the only ones, nor perhaps 
the most important ones, by which ridged beach plains are pro- 
duced; nor should the beach ridges in any case be regarded as 
the product of individual great storms, as has been so commonly 
assumed. 

It has already been shown in connection with the discus- 
sion of beach profiles of equilibrium, that a shoreline must be 
prograded wherever longshore currents of any type bring to 
it more debris than the waves there operating can remove. 
Deposition of excess debris shallows the offshore bottom, favor- 



408 SHORE RIDGES AND THEIR SIGNIFICANCE 

ing the formation of waves of translation, which in turn drive 
the bottom debris on shore until prograding of the shoreline 
and deepening of the bottom produces a profile which is in 
equilibrium with the forces there at work. If the supply of 
debris by longshore currents is kept up indefinitely, the shore 
may be extensively prograded before equilibrium is established. 
It should be noted that in the case here considered the long- 
shore currents are forced to move seaward because the shore is 
prograded, whereas in the case mentioned by Gilbert the shore 
was prograded because the currents moved seaward. Waves 
are the active agents in causing the prograding, and derive 
much of their material from the offshore bottom, as in the case 
of offshore bars mentioned by Davis. But unlike the case con- 
sidered by him, longshore currents are primarily responsible for 
a continuous supply of material which as continuously shallows 
the offshore bottom; and the prograding of the shore is not to 
be correlated with the initial bottom slope nor with storm 
waves of different sizes. The shoreline advances seaward 
throughout a considerable portion of its extent simultaneously, 
and does not grow by the longitudinal extension of each ridge, 
as in the case of compound spits. 

It is immaterial what particular type or types of currents 
bring an excess of debris to the prograding area. Beach drift- 
ing along both the shore and shoreface zones is an exceedingly 
important and commonly neglected source of supply. Where 
beach drifting is from opposite directions toward a common 
point, as not infrequently happens in bays and lakes, there will 
be an accumulation of material at the meeting point, where 
weaker or conflicting wave currents are unable to dispose of it. 
Beach drifting in but one direction along a shoreline which sud- 
denly changes its trend, will cause an excessive deposit just be- 
yond the angle in case the shore bends backward, because wave 
action upon the more protected shore around the bend is not 
sufficiently vigorous to remove all the debris deposited there 
Material drifted along bayside beaches toward the bay heads, 
shallows the latter areas and permits the small waves operat- 
ing there actively to prograde the shoreline. 

Offshore bars are characteristic of shorelines of emergence, 
and are described on an earlier page. But it will not be in- 
appropriate to consider in this connection the origin of pro- 



ORIGIN OF BEACH RIDGES 409 

graded bars showing beach ridges. Where an offshore bar has 
been formed with a profile of equilibrium nicely adjusted to the 
marine forces along its entire length, it is evident that any 
disturbance of conditions at one point along its sea front may 
lead to retrograding or prograding at another. A succession 
of storms causing unusual erosion in one locality may permit 
beach drifting or other longshore movements to carry an exces- 
sive amount of debris to another part of the bar, disturbing the 
equilibrium there and causing prograding. The opening and 
closing of inlets, by affecting longshore transportation, may 
indirectly cause retrograding or prograding on adjacent parts 
of the shore. Additions to the face of an offshore bar do not 
necessarily imply, therefore, that larger storm waves have been 
breaking on the deeper parts of an initial sloping sea-bottom; 
neither does retrograding indicate that the bar previously ad- 
vanced to the zone where the largest storm waves broke on 
the initial bottom, and that it has now entered a new stage of 
its development characterized by progressive retreat. On the 
coatrary, both retrograding and prograding must frequently 
be interpreted as horizontal oscillations of the shoreline conse- 
quent upon disturbances of the shore profile of equilibrium 
which may be very temporary in some cases, but endure for a 
considerable time in others. As will be shown in later chapters, 
parts of the Atlantic shoreline have repeatedly been retro- 
graded and prograded. It follows from these considerations 
that the retrograding or prograding of a shore does not form a 
satisfactory basis for discriminating between stages of shoreline 
development, as has been sometimes assumed. 

It may happen that an initial shallow on a shoreline of sub- 
mergence will for a long time occasion the formation of waves 
of translation, which will in turn sweep upon the shore all debris 
deposited over the shallow. A cuspate foreland may thus ad- 
vance over the shallow and finally conceal it, with the result 
that the shore will exhibit a foreland unrelated to any visible 
shore irregularity or any known currents. A river may deposit 
so much sediment opposite its mouth as to shallow the sea- 
bottom, whereupon the waves will re-establish the shore profile 
of equilibrium by eroding the bottom and prograding the shore- 
line, the latter action producing a cuspate foreland (or cuspate 
delta) showing parallel beach ridges (Fig. 126). ^ 



ill 

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beach ridges. 
Page 410 



ORIGIN OF BEACH RIDGES 411 

There is a widespread belief that the beach ridges, which 
often characterize the surface of forelands, bars, tombolos, and 
other prograded shore forms, represent the work of individual 
great storms. Men whose opinions must always carry great 
weight have either explicitly or by implication supported this 
view. Gilbert 12 is very clear in his statement: " Each of these 
(ridges) is referable to some exceptional storm, the waves 
of which threw the shore drift to an unusual height." Davis 13 
expresses much the same opinion concerning beach ridges on 
offshore bars, but adds that further study and observation are 
required to demonstrate the validity of certain points in his 
explanation of bar formation. Other authors have expressed 
somewhat different views. In discussing a paper by Redman 14 
on the shore deposits along the south coast of England, B. S. 
Howlett 15 states that every beach ridge represents " the accu- 
mulation of shingle resulting from some stormy tide," while 
Sir William Cubitt 16 " apprehended that these ' fulls ' coin- 
cided with, or at least were influenced to some extent, by the 
lunar cycles." Cornish 17 would recognize " neap tide fulls " 
and " spring tide fulls." He apparently considers that these 
tidal ridges may be amalgamated into a '"'summer full " and a 
" winter full," and that these larger fulls may in their turn 
sometimes coalesce. Unlike most observers, Wheeler 18 believes 
that the ridges were built up during calm weather. Solger 19 
advances the theory that in the case of dune ridges, which as 
we shall see later are essentially beach ridges capped by sand 
dunes, each ridge was formed during a dry climatic period, 
when the sand of a prograding shore was blown back to the 
line of ridge formation; while the intervening swales represented 
wet periods during which vegetation advanced rapidly over the 
newly gained land and prevented the sand from being blown 
into dunes. Three dune ridges are supposed by Solger to be 
formed each century, each of which corresponds to the dry 
phase of the well-known 35-year climatic period of Bruckner. 
Keilhack 20 estimates that at Swinepforte one ridge has formed 
in every 35 years on the average, and he follows Solger in corre- 
lating their formation with the 35-year Bruckner cycle. 

There are several reasons for doubting the possibility of cor- 
relating individual beach ridges with a corresponding number 
of exceptional storms which cast up the shore drift to an unusual 



412 SHORE RIDGES AND THEIR SIGNIFICANCE 

height. In the first place, it is difficult to imagine the supply 
of shore debris and other shore conditions so adjusted that each 
exceptional storm would find enough material available with 
which to construct a high ridge, yet too much to permit the 
ridge to be driven back into coalescence with an earlier one 
formed by the last preceding exceptional storm. On the con- 
trary, we should rather expect that one exceptional storm might 
do no more than raise a submarine bar in front of the shore; 
a second great storm from a slightly different direction might 
wipe the bar out of existence; the bar might reform during a 
third storm of equal violence; moderate waves in calmer weather 
might then raise the surface of the bar into a ridge a number 
of feet above sealevel; the next great storm might produce a 
new bar in front of the one just formed; and so on. In this 
imaginary case there occurred four exceptional storms, but there 
are only two beach ridges; and one of these was not raised above 
the sea by any of the storms. Observation will show that many 
beach ridges when followed along their crests subdivide into 
two or more ridges. Manifestly, if the separate ridges be re- 
garded as the work of several exceptional storms, the compound 
ridge cannot properly be regarded as the work of one storm. 
The number of ridges formed in a given time do not correspond 
with the expectable number of great storms within that period. 
Thus the 121 ridges of the Darss foreland in Germany have 
been built in a period estimated to be from 3000 to 6000 years 
which would mean an average of only one great storm in 
every 25 or 50 years. If the time required for the develop- 
ment of Nantasket beach has been correctly estimated by 
Johnson and Reed 21 one would have to suppose that only one 
great storm in several centuries has been recorded by the beach 
ridges in the southern half of that district. 

It is clearly impossible to suppose that every great storm 
builds a beach ridge, for observation abundantly proves the 
contrary. Indeed, I know of no case in which a typical com- 
plete beach ridge of large size has been wholly produced by one 
storm, although I do not regard this as impossible. On the 
other hand, a large part, if not all, of a beach ridge is often 
swept away during a single exceptional storm. We cannot 
suppose that every beach ridge represents the work of one 
exceptional storm, since, as has been shown, such a ridge often 



ORIGIN OF BEACH RIDGES 413 

represents the combination of several ridges elsewhere distinct, 
I do not believe that one should even regard a given beach 
ridge as necessarily the product of several exceptional storms; 
for while unusually high beach ridges must have been subjected 
to the influence of waves of sufficient magnitude to cast debris 
to their crests, the majority of ridges could have reached their 
present height through the influence of ordinary storm waves, 
and many of them perhaps by very moderate wave action at 
high tide. It is even possible to suppose that on a given beach 
plain none of the exceptional storms of the past are recorded 
by any of the ridge crests, but only the more prolonged activities 
of less violent wave action. 

The height of a beach ridge depends in part upon the size of 
waves, but in part also upon other factors, among which may 
be mentioned rapidity of supply of material, and the relation 
of the new ridge to pre-existing ridges. If longshore currents 
supply debris with great rapidity, the shoreline may be pro- 
graded so fast that a given beach ridge has little opportunity 
to grow to a great height before the shoreface zone is shallowed 
and a new ridge begins to form in front of it. A number of 
ridges of moderate height might thus be formed in the intervals 
between exceptional storms. Continued shallowing of the off- 
shore zone due to rapid deposition would also tend to change 
the largest storm waves into smaller waves of translation before 
they reached the line of ridge building, with the result that 
even great storm waves might not build high ridges. Less 
rapid supply of shore debris would favor the building of higher 
ridges in several ways: waves could cast material upon the 
ridge nearly as fast as it was supplied, enabling a ridge to grow 
to its full height before sufficient change occurred in the shore 
profile to require the initiation of a new ridge farther seaward; 
great storm waves would have a better opportunity to reach 
the shoreline, and the longer life of a ridge at the shoreline 
would increase the chances of such waves assisting in its con- 
struction; and while slower debris supply would increase the 
danger of ridge removal by storm waves, it would also increase 
the chances that wave attack might drive the shoreward ridge 
back upon the one behind it, thus forming a compound ridge of 
greater height. It can hardly be doubted that many of the 
prominent beach ridges of prograded shores represent the accu- 



414 SHORE RIDGES AND THEIR SIGNIFICANCE 

mulations of many subordinate beach ridges successively formed 
in front of a main shore ridge and later driven back upon it. 

The future of any given beach ridge is very uncertain, because 
of the variable nature of the marine forces operating upon a 
prograding shore. It may have its further growth arrested by 
the development of another ridge in front of it; it may be com- 
pletely washed away by the next storm; it may grow until it 
acquires large size and permanence of position; or it may be 
driven back to coalesce with one or more earlier ridges. A 
ridged beach plain is thus a very imperfect record of a complex 
history : only a fraction of the ridges once formed are preserved ; 
the records of many storms are forever lost; some of the re- 
maining ridges may record one great storm, others certainly 
represent the work of many different wave attacks upon the 
same line, while still others are composed of two or more formerly 
independent ridges forced into coalescence. One may admit 
that beach ridges can be materially affected by great storms, by 
spring and neap tides, by summer and winter storms, and pos- 
sibly even by a 35-year climatic cycle; but he must still, recog- 
nize the impracticability of correlating a given series of ridges 
with a given succession of any of these phenomena. 

Rate of Beach Ridge Formation. — The student of shorelines 
often desires to secure an approximate idea of the length of 
time which has elapsed since the sea worked upon a certain 
part of the coast, and a succession of beach ridges sometimes 
affords the best available data. It is occasionally possible to 
determine the time occupied in building a certain number of 
the latest ridges, and if the rate were uniform throughout the 
growth of the entire beach plain the problem would be a simple 
one. From what has been said, however, it is evidently far 
from safe to assume that the older ridges were formed at the 
same rate as those of later date. The history of a beach plain 
is too complex, and its record preserved in too incomplete a 
manner, to enable one to say how few or how many ridges have 
been eliminated by erosion or coalescence. Furthermore, the 
rate of debris supply must vary with time, and the increasing 
depth of water encountered as the plain builds forward into 
the sea must affect its rate of growth. There are, nevertheless, 
certain general principles which may guide one in endeavoring 
to reach a reasonable conclusion as to the approximate time 



RATE OF BEACH RIDGE FORMATION 



415 




416 SHORE RIDGES AND THEIR SIGNIFICANCE 

represented by a given series of ridges; these may be stated 
categorically, with such comments as seem necessary. 

1. Short ridges normally require less time than longer ones. 
Thus a series of short ridges representing successive recurved 
points at the end of a spit may succeed each other with rapidity, 
since all the debris carried along the shore is concentrated at 
the narrow end of the spit. The same amount of debris em- 
ployed in prograding a long stretch of the shoreline would 
build very few long ridges in the same length of time. Rock- 
away Beach, near the entrance to New York Harbor, is a good 
example of a compound recurved spit which is growing west- 
ward at a fairly rapid rate by the addition of successive recurved 
ridges of small height at its distal point. As will appear from 
Figure 127, reproduced from survey charts and reduced to a 
common scale by the Metropolitan Sewerage Commission of 
New York City, the westernmost ridge of the 1889 chart was 
diminished in area and two new ridges were added before the 
survey of 1905. Seven years later three additional ridges had 
been formed. In other words, five ridges were formed in twenty- 
three years, the average rate of growth varying from one ridge 
in eight years to one ridge in a little more than two years. The 
actual increase in the length of the spit during the whole period 
was nearly one mile, or an average annual advance of over 
200 feet. 

2. For a given exposure, low and narrow ridges imply a 
smaller lapse of time than an equal number of high, broad 
ridges. This depends upon the fact already explained that 
rapid supply of debris tends to cause a rapid prograding of the 
shoreline, with opportunity for low and narrow ridges only to 
form. 

3. One series of parallel ridges abruptly truncated by another 
series trending in a different direction (Plate XLVIII), does not 
necessarily imply a longer lapse of time than would a single par- 
allel series containing the same total number of ridges. This will 
be apparent from Figure 128. Let us imagine that a projecting 
headland, with the shoreline 0, 0, is cut back on its north side to 
the new shoreline 1, and that the eroded debris is deposited on 
the east to form the beach ridge 1'. Later erosion cuts the shore 
farther back to 2, thereby removing the extreme northern end of 
the beach ridge 1', while deposition of the eroded debris forms beach 




Fig. 127. — Successive stages in the development of Rockaway sand 
spit, Long Island. 

Page 417 



418 



SHORE RIDGES AND THEIR SIGNIFICANCE 



ridge 2' '. This process is repeated, until erosion drives back the 
shore to 5, thereby truncating the northern ends of beach ridges 
numbers 1' to 4' inclusive, and deposition forms beach ridge 5', 
Owing to a change in the balance of shore processes, possibly 
consequent upon a change outside of the area shown in the 
figure, deposition replaces erosion on the north, and the beach 




6 , T'2''3'V5 ? 6 , 7 V 8' 

Fig. 128. — Diagram of cliffed headland and associated beach ridge plain, 
showing that one series of ridges truncating another does not necessarily 
imply a longer lapse of time than an equal number of parallel ridges. 



i 



ridge 6, 6' is formed all around the headland, being followed by 
ridges 7, 7' and 8, 8'. We now have on the north one series of 
parallel ridges which abruptly truncates another series; yet no 
greater time is here represented than that represented by the 
continuously parallel series V to 8' measured toward the east. 
It is not safe to assume, as has sometimes been done, that where 
one series of ridges truncates another, allowance must be made 
for a large time interval at the break. Discordance of ridge 
direction may or may not imply a greater lapse of time than 
accordance. 

4. Dune ridges, or parallel ridges of dune sand corresponding 
in all respects with beach ridges, except as regards details of sur- 
face form, are to be regarded as resting upon true beach ridges, 
and may be used as readily as the latter in interpreting shoreline 



RATE OF BEACH RIDGE FORMATION 419 

changes. The regularity of crestlines and parallel arrangement 
of the dune ridges in such regions as the Darss foreland and 
Cape Canaveral (Fig. 129) leave no doubt that they are lines of 
shore dunes which have formed on the successive beach ridges 
when each ridge was next to the sea. Trenches cut through 
dune ridges have revealed the presence of beach sands or gravels 
below. That the dune ridges have not moved from their initial 
position is evident, for had they done so their crests would have 
become very irregular and would necessarily have lost their 
beautiful parallelism. On Cape Cod, where the dunes of the 
Provincelands have migrated under the influence of the winds, 
their former parallelism is lost and the position of the beach 
ridges is scarcely determinable. The idea, sometimes advanced, 
that the ridges are merely lines of shore dunes which have 
rolled inland from a stationary shoreline like waves of the sea, 
will not commend itself to those familiar with the phenomena 
of dune migration. Since the dunes must have formed in place 
on beach ridges at the shore, there must have been time enough 
in each case for a beach ridge to be formed by the waves; prob- 
ably also for enough vegetation to gain a foothold on the ridge 
to arrest windblown sand coming from the beach and so prevent 
its being carried over into the swale or slash back of the ridge; 
and, finally, for the dune sand to accumulate in sufficient quan- 
tity materially to augment the height of the ridge. Long, 
broad, and high dune ridges, like those of the Darss or Canav- 
eral, must have required many years for their construction. 

5. While a large number of beach ridges indicates the lapse 
of a long time interval since the first one was formed, the con- 
verse is not true. On a graded shoreline, where neither pro- 
grading nor retrograding is occurring, a single beach ridge may 
represent the slow accumulation of many centuries. Not in- 
frequently two or three beach ridges on one part of a shore rep- 
resent the same time interval as does a large series of beach 
ridges on a closely adjacent part of the shore. It is not permis- 
sible, therefore, to assume a short time interval for the building 
of narrow beach plains containing but few ridges. 

Dungeness Cuspate Foreland. — It may not be without interest 
to review some of the data available as to actual or estimated 
rates of beach ridge and dune ridge formation. The Dungeness 
of southeastern England is a prominent cuspate foreland project- 



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Fig. 129. — Ridges of the Cape Canaveral cuspate foreland. For the most 
A part they are dune ridges, but beach ridges little altered by wind action 
occur near the Light. 

Page 420 



RATE OF BEACH RIDGE FORMATION 



421 




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422 SHORE RIDGES AND THEIR SIGNIFICANCE 

ing from a curved reentrant of the shore and measuring about 
15 miles along either side, its seaward portion consisting of a 
splendid series of shingle beach ridges. Between certain groups 
of the ridges are broad belts of marsh, while the base of the fore- 
land consists almost wholly of marshland formed by the silting 
up of an extensive bay, which formerly occupied the interior of 
an initial compound cuspate bar. As a rule the shingle ridges 
are covered by very little vegetation, although some of the older 
ones are grassed over; while belts of grass and broom occupy 
many of the swales, thereby emphasizing to the eye the ridged 
character of the surface. (Plate XLIX.) In general appearance 
the ridges and swales closely resemble the well known " Wallen" 
and " Rinnen " of the island of Rugen (Plate L) described and 
figured by Braun 22 . So far as I could judge without careful 
measurements, the ridge crests of the Dungeness are prevailingly 
of moderate height, possibly rising 3 to 6 feet above intervening 
swales and 8 to 12 feet above high tide, where typically devel- 
oped. Occasional sandy ridges are encountered, but well rounded 
flint shingle is the only material found in most of the ridges. 

As shown by the map (Fig. 130) the older ridges have clearly 
been truncated by wave erosion on the south side of the fore- 
land or " ness," and the erosion products built into additional 
ridges at the point and along the east side. Two miles west of 
the point the ridges show a complex arrangement over a broad 
area, but along a line drawn from Lydd to the point of the ness 
the succession of ridges is fairly regular. During the reign of 
Elizabeth, the distance from Lydd church to the extremity of 
the point was three miles, according to Redman 23 . In 1860, as 
shown by sheet No. 4 of the Geological Survey of Great Britain, 
this same distance was nearly four miles, indicating that the 
point advanced seaward about one mile in a little less than three 
centuries, which is equivalent to an annual advance of a little 
over 6 yards. Redman 24 studied the rate of advance as indi- 
cated by various lines of evidence accessible to him in 1852 and 
concluded " that the average annual increase, during two cen- 
turies has at least amounted to nearly 6 yards." Drew 25 found 
that from 1794 to 1860 the annual advance was about 5 J yards. 

There are about 25 beach ridges shown on Drew's map (Sheet 
4, Geological Survey of Great Britain), as crossing the last mile 
of the distance from Lydd to the point of the ness. Although 



RATE OF BEACH RIDGE FORMATION 



423 




424 SHORE RIDGES AND THEIR SIGNIFICANCE 

Drew states that south and southeast of Rye the ridges are more 
numerous than could be shown upon the map 26 , in discussing 
the changes near the point of the Dungeness he says that he 
" inserted all the ' fulls ' or shingle ridges on the previously 
featureless Ordnance map 27 ." Gulliver 28 counted twenty-three 
'' successive shorelines" on the east side of the ness between 
Lydd and the sea, and as the ridges there cover a breadth 
of about a mile, and are shown by the Ordnance map to be 
between 20 and 25 in number, it would seem fair to assume 
that near the point of the Dungeness one ridge was built on an 
average every 11 or 12 years. It should be noted that some of 
the ridges, especially those closest to the point, are short, and 
that they are formed of material easily and rapidly secured from 
the south side of the ness which has long been suffering active 
erosion; both of which facts would lead us to expect an unusu- 
ally rapid development of ridges near the point. That this has 
been the case is suggested by Redman's observation in 1852 
that the point had advanced with unusual rapidity during the 
two years previous to his study 29 , although the period is too 
short to be very significant. One of the coast guards stationed 
on the south shore of the ness informed me that the sea had re- 
moved their lookout house and cut that part of the coast back 
50 feet within recent years, while the east side of the ness was 
advancing about 20 yards annually. This is in apparent dis- 
agreement with Gulliver's statement in 1897 that recent obser- 
vation indicated an annual advance of but 1J yards 30 ; but both 
figures may be correct for limited periods. \ 

The second edition of Lewin's " Invasion of Britain by Julius 
Caesar 31 " contains an interesting map, reproduced by Burrows 32 
in his volume on Cinque Ports, which shows the location of 
marshy lands on the Dungeness reclaimed previous to the 14th 
century. From this map it appears that the Denge Marsh, 
east of Lydd, was dyked about 774 A.D. Since this marsh 
could hardly have come into existence until at least one beach 
ridge had formed to the east of the present position of the marsh 
to shut out the vigorous waves incident to such an exposed 
locality, it would appear that the ridges east of Lydd, already 
stated to be 23 in number, have been formed in the interval 
between a date previous to 774 and the present time. This would 
mean an average of about 50 years for the construction of each 



RATE OF BEACH RIDGE FORMATION 



425 



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426 SHORE RIDGES AND THEIR SIGNIFICANCE 

beach ridge. Drew 33 considers that the region east of Lydd 
was open sea up to the tenth or eleventh centuries, and while 
his arguments are not wholly conclusive on this point, it may 
be noted that on the basis of his interpretation each ridge re- 
quired not more than 35 to 40 years for its construction. That 
the older ridges southwest of Lydd are of considerable an- 
tiquity is indicated by the weathered character of their com- 
ponent pebbles 34 . 

An attempt has been made to show that the Dungeness did 
not exist at all in the time of Julius Caesar, and Appach 35 
gives a map of the supposed condition of this part of the English 
coast in the year 55 B.C. upon which the foreland does not 
appear. Should this contention be valid, then the ridges of the 
Dungeness, numbering in 1860 at least 135 according to a map 
which probably does not show the full number, must all have 
formed within an interval of little more than 1900 years; or at 
an average rate of one ridge in 14 years. There are ample 
grounds for rejecting Appach's conclusions, however. He did 
not properly understand the processes by which the Dungeness 
was formed, and his methods of reasoning are unconvincing. 
The fact that certain towns formerly seaports are now far 
inland, upon which he bases some of his arguments in favor of 
the recent construction of the foreland, is readily explained 
by Lewin's map which shows navigable bays back of the beach 
ridges of Dungeness point. The towns were located upon 
bays, which have since silted up and been converted into 
dyked marshes. Roman remains are found extensively over 
Romney Marsh which occupies the northern half of the foreland, 
proving that a large part of the Dungeness was completed and 
under cultivation in Roman times 36 . Robertson 37 has likewise 
demonstrated that much of the Dungeness existed at this an- 
cient period. This means that the construction of the beach 
ridges of the entire foreland occupied an unknown length of 
time, certainly greater than 2000 years, and probably very 
much greater. 

The available data accordingly indicates that the rate of beach 
ridge formation on, the Dungeness foreland has varied greatly 
at different times, the average rate over a number of years 
rising as high as one ridge every 11 or 12 years at certain times 
and places, and dropping at least as low as one ridge in 40 or 50 



RATE OF BEACH RIDGE FORMATION 



427 




<1> 



428 SHORE RIDGES AND THEIR SIGNIFICANCE 

years elsewhere. One must fully recognize, however, that even 
at a given place and period the building of ridges is neither 
uniform in rate nor necessarily continuously ■' forward. In a 
series of ridges formed at the average rate of one every 12 years 
a certain ridge may have required half a century or more for 
its completion, several other ridges may all have been built 
within a decade, while still others may have been built and later 
destroyed by a temporary erosion, thereby lowering the aver- 
age rate of ridge formation for the series as a whole. For this 
reason, rates of beach ridge formation based on data covering 
very short periods are not of much value. 

Taking all the facts into consideration I am inclined to be- 
lieve that an average rate of one ridge constructed every 20 to 
40 years is probably a reasonable figure for the Dungeness as a 
whole. 

Darss Cuspate Foreland. — With the exception of Cape Canav- 
eral, the finest example of a cuspate foreland composed largely 
of dune ridges which it has been my "good fortune to see, is the 
Darss foreland northwest of Stralsund on the Baltic coast of 
Germany. Several former islands are here tied to each other 
and to the mainland by a complex tombolo, which has been pro- 
graded in front of the principal island (the Alt Darss) to form a 
triangular cuspate foreland (the Neu Darss) measuring from 7 
to 10 kilometers (4 to 6 miles) on each side. Northeasterly and 
easterly moving beach drifting, possibly aided by other currents, 
transported debris which wave action built into a series of beach 
ridges, the axis of each ridge trending first northeast and then 
eastward. After each beach ridge was constructed dry sands 
from the shore were blown upon its crest by the winds until it- 
rose into a dune ridge from one to several meters in height. As> 
the foreland grew northward into the Baltic, erosion along its 
western side removed large portions of the ridges in that direc- 
tion while redeposition of the eroded material on its northern 
side accelerated the northward advance. So much of the western 
ends of the ridges has been lost by erosion that the east trend- 
ing portions alone remain to make up most of the resulting 
truncated cuspate foreland (Fig. 131). 

Unlike the barren shingle ridges of the Dungeness, the dune 
ridges of the Darss are well forested (Plate LI), and the " Darss- 
erwald " is now protected as a hunting preserve for one of 



RATE OF BEACH RIDGE FORMATION 



429 



the German princes. The crests of the ridges rise 15 to 25 
feet above the adjacent swales in places, and occasional ridges 
and a number of individual dunes reach a greater altitude. Most 
of the ridges do not exceed a height of 10 feet above the deepest 
parts of the swales, and perhaps the greater number fall short 



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Fig. 131. — Dune ridges of the Darss cuspate foreland, Germany. 



of 6 feet. Some of the swales are deep enough to contain long 
narrow ponds, others are marshy, while still others differ from 
the pine covered ridges in having fewer trees and a grassy bot- 
tom. Ordinarily the ridges are from 75 to 150 feet apart, but 
this distance varies greatly in different parts of the Darss, 
swales between 500 and 1000 feet in breadth being known. The 
roads through the forest are sandy, and where they are cut 
through the higher ridges one occasionally sees a good "exposure 
of cross bedded dune sands, the surface layers being bleached 
by weathering in the ridges earliest formed; but ferns and 



430 SHORE RIDGES AND THEIR SIGNIFICANCE 

other vegetation usually carpet the forest floor and conceal 
the sand, making the region one of great beauty. There is 
little in the forest covering to remind one of the scrub palmetto 
and occasional palms of Cape Canaveral; but in spite of the 
contrast in vegetation, the forms of the dune ridges and swales, 
the variation in ridge height and spacing, and the greater 
weathering of the sands in the older dunes, constantly reminded 
me of identical features observed in the Canaveral ridges only a 
few months previously. 

The Darss has been briefly described by Braun 38 and at 
great length by Otto 39 . The excellent essay of the latter author, 
entitled " Der Darss und Zingst: Ein Beitrag zur Entwick- 
lungsgeschichte der Vorpommerschen Kuste," is based upon a 
comparative study of ancient and modern maps and detailed 
field investigations; and the author discusses at length the 
preglacial conditions of the region involved, the effects of gla- 
ciation and of post-glacial changes of level upon the coastal 
topography, and finally the more recent morphological changes 
of the coast including the development of the dune ridges. 
Unfortunately it is sometimes impossible to follow all of this 
author's arguments, because he commits the too common error 
of locating important features and describing essential meas- 
urements in terms of unimportant local roads, property bound- 
aries, etc., the names of which do not appear on any maps in 
his report nor on any other maps available to the ordinary 
reader. 

Otto's description of the dune ridges 40 is open to the criticism 
just mentioned; but I understand from the text that there are 
121 dune ridges distinguishable in passing from south to north 
along the western side of the Darss, only a part of which number 
are indicated on the German topographic map of the area. 
Historical evidence proves that the coast has advanced 1300 
feet (400 meters) in 200 years. Using this figure as a basis 
for calculation, and making some allowance for the fact that 
the younger dune ridges were probably built more rapidly than 
the older ones, Otto concludes that 3000' years is the shortest 
possible time in which the 121 ridges could have been con- 
structed 41 . This would mean an average of at least 25 years for 
the construction of each ridge. Otto allows 1000 years addi- 
tional for the formation and subsequent destruction of some 



RATE OF BEACH RIDGE FORMATION 431 

older ridges at the immediate base of the foreland, and thus 
arrives at the conclusion that the submergence which initiated 
the period of dune ridge formation (the " Litorinasenkung ") 
occurred at least 4000 years ago, or as early as 2000 B.C. If 
Keilhack 42 is more nearly correct in his opinion that this period 
of submergence occurred 7000 years ago, as seems probable to 
the writer for reasons which will subsequently appear, then the 
construction of the 121 ridges of the Darss occupied something 
like twice the minimum period assigned by Otto, and the aver- 
age time for building each ridge would be nearly 50 years. 

Swinemunde Tombolo. — The magnificent series of dune ridges, 
which make up the complex tombolo * connecting the islands of 
Usedom and Wollin some distance east of the Darss has been 
mentioned in many German works dealing with sand dunes, and 
is described at considerable length in Solger's " Dunenbuch 43 ." 
A strait some eight miles or more in width formerly separated the 
two islands. Northerly winds blowing across a broad stretch of 
open water would drive upon the converging shores of the islands 
vigorous waves, which would in turn cause active beach drifting 
southeastward along the northeast shore of Usedom and south- 
westward along the northwest shore of Wollin. Two spits began 
to advance into the strait, the western or Swinemunde spit tren d- 
ing nearly due south along the east shore of Usedom, while the 
eastern or Misdroy spit extended itself in a more westerly 
direction across the strait, being strongly recurved southward 
at the point. The Swinemunde spit was then extensively pro- 
graded to form a beach plain by the addition of some 80 dune 
ridges to its seaward side, the Misdroy spit meantime advancing 
by gaining 150 successive recurved points at its western end 
while its seaward side was being retrograded. When the strait 
was nearly closed, erosion truncated the northern end of the 
Swinemunde beach plain, cut back the mainland shore of Use- 
dom some distance, and possibly continued the previous trun- 
cation of the Misdroy recurved points. There followed a pro- 
grading of both the Swinemunde and Misdroy areas, by which 

* The fact that a narrow stream passes between the islands by a channel 
eroded across some of the dune ridges does not alter the fact that the islands 
are essentially connected by a beach plain which is continuous just below 
water level, even if interrupted by the stream at the surface; hence I have 
called the combined complex spits a tombolo. 



432 



SHORE RIDGES AND THEIR SIGNIFICANCE 




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RATE OF BEACH RIDGE FORMATION 433 

additional series of 30 and 40 dune ridges respectively were 
added to the northern sides of the almost united spits. Erosion 
slightly truncated these later ridges, and a third and last series 
was then added, bringing the completed tombolo to its present 
form. A narrow stream, the Swine, which flows alternately 
northward and southward is all that remains of the former 
strait, and it has so far shifted its position as to cut a great 
meander scarp into the oldest series of the Swinemunde ridges, 
as is clearly shown by the map (Fig. 132). 

Keilhack has made a careful study of this remarkable series 
of dune ridges, and has published his results in a valuable essay 
on " Der Verlandung der Swinepforte." He found the distance 
between ridge crests to vary from 130 to 150 feet where they 
were closely spaced, and from 330 to 460 feet where they were 
farther apart. In altitude the older ridges usually do not 
exceed 25 feet absolute elevation, but the earliest ridge formed 
in the third or last series reaches a height of 65 feet or more 44 . 
Of especial interest are Keilhack' s observations on the com- 
parative weathering effects in the three systems of dune ridges 45 . 
The dunes of the latest series are practically unweathered and 
retain the normal light color of the beach sands from which they 
were formed; they are, therefore, called " white dunes." Dunes 
of the next older series show a thin surface layer of bleached 
sand, below which the sand is colored yellow by limonite; these 
are known as the " yellow .dunes." Finally, the oldest dunes 
have a thin surface layer of humus from less than an inch to 
an inch or more in thickness, below which is the bleached sand 
zone from 1 to lj feet thick. Beneath the bleached zone the 
sand grains have a coating of brown limonite, and may even be 
locally cemented by this material into a soft ferruginous sand- 
stone. These " brown dunes " must have existed essentially 
as we find them for a long period of time in order to experience 
such pronounced weathering effects. The formation of the 
bleached zone is attributed to the leaching action of atmos- 
pheric waters carrying C0 2 and humus acids, by means of which 
all iron is removed from the upper foot or eighteen inches 
of each dune ridge. How clearly the white surface band is 
contrasted with the darker sand below when exposed in cross 
section, may be seen in Plate LII, which represents a road-cut 
through an old dune ridge back of the present shore at Daytona, 



434 



SHORE RIDGES AND THEIR SIGNIFICANCE 




RATE OF BEACH RIDGE FORMATION 435 

Florida. The weathering phenomena characteristic of the yellow 
dunes of Keilhack was clearly evident in the older dunes of the 
Darss, but I saw no such advanced stages of alteration as that 
author describes for his brown dunes. I am, therefore, inclined 
to agree with Otto 46 that the oldest preserved dune ridges of the 
Darss are not so ancient as the oldest ridges near Swinemunde. 
Perhaps the ridges earliest formed near the base of the Darss 
and later eroded 47 were more closely similar to the brown dune 
ridges of Keilhack. 

Through a comparison of reliable maps Keilhack has been 
able to show that between the year 1694 and the beginning of 
the twentieth century the shore west of the northern outlet of 
the Swine was prograded nearly one mile (1500 meters), while 
elsewhere the advance was less marked. Since 1694 six dune 
ridges have been formed, or an average of one ridge in every 
35 years. The author then points out that this figure agrees 
so remarkably with the figure found by Bruckner for a periodic 
climatic oscillation, that one cannot well refuse to accept Sol- 
ger's opinion in favor of a genetic connection between the 
formation of parallel dune ridges and this climatic period. He, 
therefore, accepts 35 years as the time represented by each 
ridge, and derives a chronology for the entire tombolo. East of 
the Swine, the 150 ridges of brown dune forming the original 
Misdroy spit would require 5200 years; the 40 ridges of yellow 
dunes which followed would demand 1400 years; and the 7 or 8 
ridges of white dunes about 300 years additional; making a total 
of 7000 years for the entire series of dune ridges on the Misdroy 
side of the tombolo. The number of ridges on the Swinemunde 
side is much less, but the record there is assumed to be less 
complete. 

To the 7000 years derived in the manner above indicated, 
Keilhack would add an unknown number of years representing 
two erosion periods which separated the three systems of dune 
ridges. The evidence for two erosion periods, distinct from the 
periods of prograding, is not convincing, and Keilhack's discus- 
sion of this question does not appear to be consistent. To 
account for the truncation of the northern ends of the Swine- 
munde brown dunes previous to the formation of the next 
following series of yellow dunes, he invokes a subsidence of 
the entire district, amounting possibly to as much as 6 to 10 



436 SHORE RIDGES AND THEIR SIGNIFICANCE 

feet, which would decrease the supply of marine sand for dune 
building and favor erosion 48 ; at the end of the erosion period, 
estimated as 1000 to 2000 years in length, it seems that re-ele- 
vation is considered a probable though not necessary cause of 
the resumption of ridge building which resulted in the next 
series of yellow dunes 49 . Inasmuch as coastal subsidence is 
appealed to in order to account for the cessation of ridge build- 
ing and the initiation of erosion on the Swinemunde portion of 
the area, it would seem natural to expect that the subsidence 
would effect the same changes on the Misdroy hook just across 
the Swine. But since the Swinemunde hook has but 80 ridges, 
and the Misdroy hook 150 ridges in the oldest series, it is evi- 
dent that according to Keilhack's interpretation the Misdroy 
hook must have continued to advance for 2400 years after subsi- 
dence is supposed to have arrested the advance of the Swine- 
munde hook; indeed, Keilhack specifically states that the ero- 
sion which truncated the Swinemunde hook may very well have 
occurred during the same 2400 years that the Misdroy hook was 
still advancing 50 , apparently not realizing that this invalidates 
his previous arguments in favor of repeated depressions and 
re-elevations of the area as a cause of alternate periods of shore- 
line erosion and deposition. To account for the cessation of 
the building of the yellow dunes, their truncation by erosion, 
and the later building of the white dunes, Keilhack imagines a 
second movement of subsidence, introducing an erosion period 
some hundreds of years long, followed probably by a slight 
elevation which occurred between 1500 and 1600 A.D. and ex- 
posed great masses of sand on a wide beach which the wind 
could build into the especially high dune ridge which marks the 
beginning of the white dune system 51 ; but on the following page 
of his essay he states that the eastern half of the Swinemunde- 
Misdroy region continues to be eroded up to the present day. 
Thus this author invokes coastal subsidence in order to account 
for shoreline erosion, yet recognizes such erosion following coastal 
elevation. 

The reasons for rejecting the oft-repeated opinion that shore- 
line erosion implies coastal subsidence have already been discussed 
at some length. In the opinion of the present writer all of the 
phenomena described by Keilhack as characteristic of the Swine- 
pforte dune ridges are readily to be explained without invoking 



RATE OF BEACH RIDGE FORMATION 437 

any changes in relative level of land and sea. Beach ridges and 
dune ridges have in the past been built forward at one place and 
truncated in another simultaneously, just as the Dungeness is 
today having its ridges of shingle cut away on the south side and 
built forward on the east; or as Cape Canaveral is being eroded 
on the east, and prograded on the south; or, indeed, as the white 
dunes near Swinemunde have been built forward in the same 
time that the closely adjacent coast was cut back. In fact, the 
erosion at one place causes, or at least accelerates, the forward 
building at another by increasing the supply of shore debris. 
It is to be expected that progressive addition of beach or dune 
ridges will in time so change the outline of the shore and hence 
the intensity and direction of marine forces, that the profile of 
equilibrium on adjacent parts of the shore will be disturbed, and 
erosion will replace deposition at certain points, without any 
change in land or sea level and without any profound revolu- 
tion in the nature of the marine forces operating on the shore. 
The equilibrium of a shore profile is a very delicate thing, and 
it may very easily be so disturbed that an excess of erosion 
replaces a former excess of deposition. 

It is highly probable that much if not all of the erosion of 
dune ridges which occurred in the Swinepforte district took 
place while dune ridges were forming in other parts of the area; 
and that, therefore, no additional time is to be allowed for these 
erosion intervals. Keilhack recognized the uncertainty of the 
erosion intervals, and, therefore, permitted his estimate of 7000 
years to remain unchanged, merely stating that the time interval 
sixice the Litorina submergence which introduced the period of 
ridge building must be more than 7000 years. 

We may accept Keilhack' s estimate of 35 years as the average 
time required for the construction of each of the six ridges of 
white dunes formed since 1694, without agreeing to the cor- 
relation of dune ridge development with Bruckner's climatic 
cycle, or to the proposed chronology of the older dune ridges. 
We have already seen that the physical forces which control 
the growth of successive beach and dune ridges are so impor- 
tant in magnitude and so variable in their activities that they 
would scarcely be materially affected by the very moderate 
climatic changes of the 35 year period. It is true that Kriiger 52 
in his study of " Sturmfluten an den deutschen Kusten der 



438 SHORE RIDGES AND THEIR SIGNIFICANCE 

westlichen Ostsee " reaches the conclusion that periods of fre- 
quent " storm tides " alternate with periods in which their 
occurrence is rare, and that these periods correspond in a gen- 
eral way with the dry and wet periods respectively of the 
Bruckner cycle. There are, however, striking exceptions to 
Kriiger's rule which cast some doubt on its value and certainly 
invalidate it for use in establishing a beach ridge chronology. 
There seems to be no escape from the conclusion that the supply 
of sand, the intensity and frequency of great storms, the length 
and position of the ridges, and other controlling factors have 
varied so greatly during the building of the Swinemunde-Misdroy 
tombolo that the average time for ridge building has been very 
different at different places and at different periods. Thus it is 
not impossible that the 150 short recurved points of the original 
Misdroy spit were built in nearly the same length of time as 
the 80 longer ridges which were added to the front side of the 
Swinemunde spit, even though the cutting of the meander 
scarp in the Swinemunde series suggests that the Misdroy spit 
may have added a few of its recurved points after the Swine- 
munde ridges were completed, thereby deflecting the Swine 
against the latter. 

The Swine has built a beautiful delta into the Haff south of 
the tombolo, and it seems probable that it carries an appre- 
ciable amount of debris into the bay on the north when it flows 
in that direction. If so, wave action should utilize this debris 
to prograde the shore with unusual rapidity near the Swine 
mouth. The existence of moles or jetties on either side of the 
mouth may also tend to check longshore transportation and to 
accelerate prograding in that vicinity. As shown by Figure 132, 
there is a delta-like projection of the dune ridge series at the 
mouth of the Swine, where formerly an embayment existed as 
shown by the older ridges; and Keilhack states that the moles 
at the mouth of the Swine have made the shore build forward 
there much more rapidly than usual during the last two cen- 
turies 53 . The six dune ridges built within this same period, and 
used by Keilhack as a basis for his calculations, may, therefore, 
represent a much smaller time interval than six ridges of the 
older series. Many of the latter may have required an average 
of 50 years or more for the construction of each ridge. 

Enough evidence has been presented to show the impossi- 



BEACH RIDGES AS RECORDS OF CHANGES OF LEVEL 439 

bility of building up any accurate chronology on the basis of 
beach ridges or dune ridges. On the other hand, it appears that 
a large series of extensive ridges must represent a long time in- 
terval, and that 25 to 50 years is not an improbable figure for 
the time required to build such prominent ridges as are character- 
istic of the Dungeness, Darss, and Swinepforte areas. Beach 
and dune ridges, therefore, have a great value in acquainting 
us with the order of magnitude of the minimum time involved 
in their construction, even though they cannot furnish more 
precise data. 

Beach Ridges as Records of Changes of Level. — A well- 
developed series of beach ridges may have a high value as evi- 
dence of former changes in relative level of land and sea, or of 
coastal stability. If there is a gradual emergence of the land 
during the development of the ridges, it would seem that the 
crests of older members of the series should be found at pro- 
gressively higher elevations above water level; whereas con- 
tinued submergence should be indicated by a decrease in crest 
altitude as one passes inland from the modern ridges. Coastal 
stability, on the other hand, should be recorded by a general 
agreement of ridge crest altitude throughout the series. 

If applied with discrimination and with a full understanding 
of the different conditions which determine the altitudes of 
beach ridges, the above principle may throw valuable light on 
the interesting questions relating to past changes in the level of 
land and sea. Its indiscriminate and uncritical use will often 
lead to erroneous conclusions. It behooves us, therefore, to 
take cognizance of certain fundamental facts concerning the 
formation of beach ridges, and to note in what ways they may 
affect our judgment in interpreting the significance of crest 
altitudes. Again it will be most convenient to state the facts 
categorically, and comment on them as may seem desirable. 

1. The terminal points of recurved spits normally descend 
toward their distal ends and pass under the water level, as has 
previously been shown. In a compound recurved spit, there- 
fore, it will often be found that the ridges back of the present 
shore, representing successive recurved points, are materially 
lower than the modern beach ridge. It is difficult to see how 
any one could regard such difference in ridge crest elevation as 
an evidence of coastal subsidence; yet it has been so regarded 



440 SHORE RIDGES AND THEIR SIGNIFICANCE 

by several observers. One should clearly realize, however, that 
the point of a spit which curves back into more protected and 
quieter waters thereby escapes that direct impact of the larger 
waves which is necessary to heap up the sand or gravel to the 
greatest altitudes; and that the failure of an adequate supply 
of debris near the terminus necessitates a low embankment in 
any case. Observation will suffice to show that where the 
points of such spits are lengthening from year to year, they are 
built low in the first place, and do not acquire their low level 
by subsidence. 

2. Beach and dune ridges of great linear extent normally 
vary in altitude along their crests. If they possess free ends, 
they usually descend more or less gradually and pass under the 
water; for while they may not recurve into quieter water, such 
unattached ridge ends resemble spits to the extent that the 
supply of debris at their distal points is insufficient to build up 
a submarine embankment and raise it to a considerable eleva- 
tion above sealevel. It is not necessary, for example, to regard 
the descending southern end of the oldest Swinemunde ridges 54 
as an evidence of coastal submergence. Variations in supply 
of material, in exposure to wave action, in depth of offshore 
bottom, and in other factors may cause a marked variation in 
crest altitude anywhere along the course of the dunes. On 
the Darss foreland, where observations indicate long-continued 
coastal stability, a large number of the older east-west dune 
ridges are low in the central part and high at either end. 

3. Successive beach and dune ridges normally differ from 
each other in altitude of crest line. This follows from what 
has already been said regarding the origin of such ridges. A 
temporary excess of shore debris may cause a new ridge to 
form before the earlier one behind it had acquired any consid- 
erable altitude; and the new ridge may rise to a great height 
before the development of a still later ridge checks its growth. 
Temporary retrograding of the shoreline may combine several 
low ridges into one high one, while earlier and later ridges re- 
main of moderate altitude. The great variability of the marine 
forces causes the successive positions of the shoreline to be 
maintained for unequal lengths of time, and to have unequal 
quantities of shore debris cast into shore ridges of unequal 
height. It may happen that one ridge is not raised above 



BEACH RIDGES AS RECORDS OF CHANGES OF LEVEL 441 




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442 SHORE RIDGES AND THEIR SIGNIFICANCE 

water level before another is built in front of it, but as a rule 
the differences in height are all to be measured above the level 
of the sea. Beach ridges are formed directly by the waves, and 
cannot, of course, exceed the height to which waves in a given 
exposure are capable of raising the material of which the ridges 
are composed. This may be only three or four feet in a sheltered 
locality, but very commonly amounts to 10 or 15 feet for ordi- 
nary shingle beach ridges on an open coast, and a single semi- 
permanent ridge like the Chesil Bank on the exposed south 
coast of England may reach a height of 40 to 50 feet above 
high water 55 , ft is no uncommon thing to find beach ridges 10 
feet or more in height irregularly interspersed with others less 
than half as high; and theoretically the difference may be as 
great as, or greater than, the maximum height of the ridges 
above water level. Practically, however, the irregular varia- 
tions in crest altitude are commonly not much greater than half 
the altitude of the higher ridges, and in many cases are appre- 
ciably less. Goldthwait 56 has described a case in which a series 
of sixteen consecutive ridges having an average crestline alti- 
tude of 3.82 feet above high water contained no ridge higher 
than 4.64 feet nor any lower than 3.04 feet; an extreme differ- 
ence of but 1| feet. 

Dune ridges owe their height to the action of the wind, and 
may, therefore, rise well above the upper reach of storm waves 
for a given exposure. Dune ridges 65 feet high are known 57 on 
the shores of the Baltic, and the remarkable height of nearly 
300 feet is reported from the somewhat irregular dune ridges 
along the coast of the Landes in France 58 . Usually, however, 
15 to 25 feet is the upper limit for individual members of an 
extensive series of dune ridges. As is to be expected, variations 
in altitude among different ridges of a given dune system are 
greater than in the case of beach ridges, because to the variable 
factors affecting the initial beach ridge upon which the dunes 
stand are added the variable factors which affect dune accumu- 
lation, including strength and direction of the winds which move 
the dry sands of the upper part of the beach, and the character 
of the dune vegetation. Twelve dune ridges, associated with 
the very accordant beach ridges described by Goldthwait and 
mentioned above, were found by that author to vary from 3.91 
to 9.04 feet in height above high water 59 . Dune ridges on the 



BEACH RIDGES AS RECORDS OF CHANGES OF LEVEL 443 

Darss vary in altitude from 2 feet or less to 25 feet or more, 
measured from the bottom of adjacent swales. Among the 
Swinemtinde dune ridges are many 3 to 6 feet high, others 25 
feet or more, and one or two as high as 65 feet above sealevel. 
The Cape Canaveral dune ridges vary from 2 to 12 feet above 
high tide level. Perhaps the lowest dune ridges are merely 
beach ridges with the surface sands slightly disturbed by the 
wind. 

It is manifestly impossible to regard such variations in the 
level of individual beach ridge and dune ridge crests as indica- 
tions of elevations and subsidences of the land. Probably no 
one would be so bold as to imagine such a rapid and oft-repeated 
alternate rising and falling of the coast as would be called for by 
the great series of ridges of the Dungeness, Darss, Swinemtinde, 
and Canaveral beach plains, were variations in ridge height to 
be regarded as proving variations in sealevel. It follows that 
one should be equally cautious in accepting the inequality in 
height of two or three ridges as a proof of changes of level; for 
if many ridges may acquire unequal altitudes without the aid 
of vertical movements of land or sea, certainly a few may do so. 
If we are satisfied as to the validity of this conclusion, we shall 
have no difficulty in realizing the fallacy of one of the lines of 
argument not infrequently advanced in support of theories of 
coastal subsidence and elevation. 

4. In a given series of beach or dune ridges there is a tendency 
for those first formed to have a lower altitude than later members 
of the series. Cornish 60 was of the opinion that "it is unneces- 
sary to invoke upheaval or subsidence to account for such 
difference of level," and explained the greater height of the 
later ridges on the ground that as a foreland builds farther and 
farther out into the water it offers increased obstruction to the 
coastal currents, thus causing them to bank up the water to a 
greater height and raising the level of ridge construction. We 
may agree with Cornish's general conclusion, yet doubt whether 
the level of the water is ever sufficiently affected by foreland 
growth to account for the phenomena in question. It is evi- 
dent, however, that on a sloping bottom only small waves can 
operate near the shore, since waves break when entering water 
of a depth about equal to their height. A beach ridge built 
near the shore will tend to have a low altitude, for small 



444 SHORE RIDGES AND THEIR SIGNIFICANCE 

waves cannot cast debris to a great elevation. Waves of greater 
• height, breaking farther seaward, finally build a new ridge in 
front of the one first formed, and are able to build the crest of 
this new member of the series to a somewhat greater altitude 
than that of its predecessor. Still larger storm waves may 
build a third ridge of still greater height; and in this manner 
there is produced, as the result of normal wave action on a 
stable coast, a series of beach ridges of increasing altitude going 
seaward. There can be no doubt that this history of beach 
ridge development has been repeated in many places along our 
coasts, and it is, therefore, manifestly impossible to regard a 
landward decrease in beach crest altitude, especially in a series 
of a few ridges only, as a proof of coastal subsidence. 

During the early stages of beach ridge formation on a shelving 
sea-bottom, it is probable that the zone of ridge building is 
shifted seaward with constantly diminishing rapidity. The 
first ridge is quickly built by the smaller waves. Soon larger 
waves begin the construction of a new ridge in front of the first. 
The shoreline remains for a longer time in this new position, 
because no change will occur until the waves have built up from 
a deeper sea-bottom a ridge of sufficient height to transfer the 
shore activities permanently to a third position still farther 
seaward. We have already seen that the longer a shoreline 
remains in a given position, the greater is the probability that 
the shore ridge will be raised to a high elevation. On this 
account we may reasonably suppose that progressively slower 
advance of a shoreline often helps to produce a series of beach 
ridges whose crest altitudes decrease in a landward direction. 

A further cause of normal decrease in altitude of progressively 
older beach ridges is probably to be found in the greater weather- 
ing to which the older members of the series have been subjected. 
In the course of many centuries it seems certain that a ridge of 
gravel loosely piled up by the waves must become somewhat 
compacted; while sand ridges will be very slowly worn lower 
under the constant attack of rains and other agencies of weather- 
ing. It can hardly be supposed that in the course of a few 
thousand years such changes in crest altitude would be very 
pronounced; but we may fairly assume that they would be 
appreciable, and might therefore serve to augment similar dif- 
ferences due to other causes. 



BEACH RIDGES AS RECORDS OF CHANGES OF LEVEL 445 

Dune ridges formed on low beach ridges, and dune ridges that 
have had only a short time in which to accumulate by reason 
of a rapid prograding of the shore, or that have been acted 
upon by the weather for thousands of years, tend to have a low 
crest altitude. From what has been said regarding beach 
ridges it follows, therefore, that successive dune ridges with 
diminishing crest heights going inland may be a normal feature 
of a stable coast, and that they are no more to be regarded as 
proofs of coastal subsidence than are beach ridges showing 
similar relations of crest lines. 

It should be fully understood that beach and dune ridges of 
progressively decreasing altitude landward are normal, but by 
no means necessary, features of a prograding shore. They are 
more apt to characterize the earliest stages of shore prograding, 
and we must be prepared to find the oldest members of a large 
series of ridges, or all the members of a very small series, showing 
the phenomenon in question at various places along a shore 
which has experienced no change of level since ridge building 
began. On the other hand, the conditions which determine 
shoreline development are so complex and are subject to such 
variations that one cannot expect to find a simple, regular de- 
crease in crest altitude as a common feature of all beach and 
dune ridge series. On the contrary, it is only under favorable 
conditions that the tendency to produce such regular differences 
in altitude is not masked or completely overcome by other 
forces. We shall find instances in which rapid prograding of 
the shore has produced a series of low ridges next the present 
shoreline, while older ridges have a higher average elevation. 

5. Beach ridges are more valuable than dune ridges in deter- 
mining changes of level or coastal stability. This follows from 
the fact that dune ridges show greater local variations in height 
than do beach ridges, as is explained in paragraph No. 3 above. 
It is clear that safe conclusions as to past moderate variations 
of relative sealevel or past coastal stability cannot be so readily 
based upon ridges which may show wide differences of level due 
to causes independent of vertical changes in the position of land 
or sea, as they can upon ridges which normally vary within 
much narrower limits. 

6. Beach ridges and dune ridges must be regarded as incom- 
parable features, when one is seeking to determine the possi- 



446 SHORE RIDGES AND THEIR SIGNIFICANCE 

bility of past changes of level. It is not permissible to compare 
an older series of beach ridges with a later series of dune ridges, 
or vice versa, and to infer subsidence or elevation if the average 
heights of the two dissimilar series are unlike. The force which 
predominates in dune building is not the same as the force which 
predominates in beach building, and there is no reason why the 
two forces should build ridges of similar height. On the con- 
trary, dune ridges are built upon pre-existing beach ridges, and 
must, therefore, exceed the latter in altitude. Near Sandham- 
maren on the southern coast of Sweden a magnificent series of 
beach ridges is bordered seaward by a higher series of dune 
ridges; but the theory that this part of the Swedish coast is 
subsiding is disproved by evidence which I will present in an- 
other connection. A similar relation of beach and dune ridges 
on the coast of eastern Canada has been cited by Ganong as an 
evidence of coastal subsidence, although Goldthwait 61 has shown 
that the later and higher dune ridges of this region rest upon 
gravel beach ridges of the same height as the older beach ridges. 
Beach ridges may properly be compared as to altitude with other 



Fig. 133. — Beach ridges indicating coastal emergence. 

beach ridges underlying dune ridges, when their surfaces are 
sufficiently exposed for this purpose; but never with the super- 
imposed dune ridges themselves. 

7. Both beach ridges and dune ridges have a distinct value 
as records of changes of level or of coastal stability, notwith- 
standing the restrictions mentioned above. A large series of 
beach ridges which may show irregular variations in heights of 
individual crests but which is characterized in addition by a 
gradual landward increase in the average height of the ridges, 
or in the heights of the principal ridges (Fig. 133), is strongly 
suggestive of emergence. If the seaward members of the series 
have a considerable height, indicating that they have more or 
less nearly attained the maximum elevation which waves in 
that exposure can give to ridges, while the older ridges have a 



BEACH RIDGES AS RECORDS OF CHANGES OF LEVEL 447 

much greater height, the evidence may be said to furnish satis- 
factory proof of elevation. I have found such ridges on the 
northern shores of the Baltic Sea, where independent evidence 
indicates progressive emergence of the land. Care should be 
taken, however, in employing this line of evidence in those cases 
where the prograding of the shore materially reduces the width 
of the water body upon which the ridge-making waves are de- 
veloped; for the size of the waves will thereby be reduced, and 
the seaward members of the ridge series will decrease in alti- 
tude independently of coastal emergence. 

We have already seen that a few beach ridges exhibiting a 
landward decrease in crest altitude is a normal feature of a 
stable shore, and therefore must not be regarded as an evidence 
of coastal submergence. It is even probable that a large series 
of such ridges may be characterized by the same landward 
decrease of average crest altitude, due to a gradual seaward 
increase in depth of water and size of waves, and to other factors 
favoring greater crest height in the later ridges. If an exten- 
sive series of beach ridges descending landward could be traced 
to a considerable depth beneath the surface of a salt-marsh 
peat deposit composed of high tide vegetation only, which had 
protected the ridges from destruction by extending over them 
as they sank lower and lower (Fig. 134), coastal submerg- 



Fig. 134. — Beach ridges indicating coastal submergence. 

ence could be inferred with reasonable certainty. A few ridges 
at a shallow depth in the marsh would not be satisfactory evi- 
dence; for normal wave action on a stable shore might fail 
to raise the initial ridges above sealevel, while marsh deposits 
might later protect them from destruction by the lagoon waves. 
It is very seldom that the conditions which render it safe to 
employ beach ridges as an evidence of coastal submergence 
exist. In all of the cases which have come to my attention 
where a landward decrease in ridge crest height has been used 
as a proof of submergence, such use has not seemed to me justi- 
fiable, for the reason that the phenomena described might 
equally well be explained as the normal product of wave action 



448 



SHORE RIDGES AND THEIR SIGNIFICANCE 






BEACH RIDGES AS RECORDS OF CHANGES OF LEVEL 449 

on a stable coast. It may reasonably be doubted whether 
beach ridge development often takes place on a subsiding coast, 
since subsidence favors marine erosion, and is highly unfavorable 
to the prograding of shorelines. 

Where a large series of beach ridges show throughout about 
the same average crest altitude, or about the same altitude for 
the principal ridges, coastal stability is strongly indicated. If 
the older and later ridges are both about as high as the present 
waves could be expected to build them, the evidence in favor of 
long continued stability may be regarded as conclusive. There 
are two hypothetical cases which might lead to an erroneous 
conclusion, but it is probable that danger of error from this 
source would be eliminated by careful observation. One may 
imagine that on a rising coast where the earliest ridges are of 
small altitude and the later ridges progressively higher, the 
amount of elevation might just be sufficient to raise the crests 
of the first ridges into the same horizontal plane with the crests 




Fig. 135. — Hypothetical case in which beach ridges on a rising coast may 
give a false indication of stability. 

of those formed later (Fig. 135); and a careless observer might 
argue in favor of coastal stability because of the resulting equal- 
ity of crest heights. But since we are not apt to find high beach 
ridges with very narrow bases, while the low ridges formed in 
shallow water are characteristically narrow, comparison of the 
older and later ridges formed in the manner indicated should 
reveal the fact that those first formed are really low ridges 
raised high above the plane in which they must originally have 
been constructed. This is made clear by Figure 135. The case 
is improbable, not merely because the rate of emergence must be 
just enough to give the required equality of crest altitudes, but 
also because a progressively emerging shore favors the repeated 
development of small ridges rather than ridges of constantly 
increasing height. 

A second case may be imagined in which progressive sub- 
mergence carries the crests of older, high ridges nearer to water 



450 



SHORE RIDGES AND THEIR SIGNIFICANCE 



level, thereby bringing them into the same horizontal plane as the 
crests of successively lower ridges formed later. Thus, as shown 
in Figure 136, one might infer coastal stability from equality 
of ridge crest altitude in a region which had really experienced 
progressive submergence. The true history might be suspected 
from the fact that an increasing proportion of the older larger 
ridges was below marsh level or the level of lagoons caused by 




Fig. 136. — Hypothetical case in which beach ridges on a sinking coast 
give a false indication of stability. 

the submergence. This hypothetical case, is, however, even 
more improbable than the one supposed above, since it involves 
not only a special rate of subsidence and the building of the 
largest ridges in the shallowest water where only small ridges 
are to be expected, but also because submergence tends to pre- 
vent ridge building entirely and to favor the erosion of the coast. 
As shown by the figure, the formation of the smaller ridges 
demands an increasingly extensive aggrading of the deeper off- 
shore bottom, a process to which submergence is distinctly 
unfavorable. 

Widely spaced older beach ridges rising above marsh level 
back of a later series, thereby giving a superficial appearance of 
the conditions represented in Figure 136 must not be regarded 
as an indication of subsidence, since such ridges may have been 
formed with wide spaces of water between them in the first 
instance, and the lagoons converted into marshes at a later date. 
Several ideal profiles through beach and dune ridge series formed 
on stable coasts are shown in Figure 137. 

Two ridges (Fig. 137 c) of similar altitude may be sufficient 
to prove long continued coastal stability, providing they are so 
high as to preclude the possibility that the earliest one was built 
much higher and later carried down by subsidence, and providing 
also the older one is manifestly not a small initial ridge raised to 
its present height by coastal elevation. In addition, there must 
be some means of proving the lapse of a long interval of time 
between the building of the two ridges. A case of this kind is 



BEACH RIDGES AS RECORDS OF CHANGES OF LEVEL 451 

presented by Nantasket Beach, Massachusetts, and has been 
fully described by Johnson and Reed. 62 

An extensive series of dune ridges may furnish reliable evi- 
dence of essential coastal stability, if their formation has evi- 
dently required so long a period of time that any marked change 





Fig. 137. — Types of beach ridges formed on a stable coast. 

(a) Earliest beach ridges lower because of shallow water nearest the original 

shoreline. 

(b) Similar to a, but older ridges isolated in marsh. 

(c) Central ridges low because of rapid prograding to present zone of wave 

action, where the tendency to prograde is much less pronounced. 

(d) Later ridges with greater average height than older, because former are 

dune ridges surmounting beach ridges, while latter are unmodified 
beach ridges. 



of level must of necessity have resulted in a pronounced differ- 
ence in crest heights recognizable in spite of individual varia- 
tions in ridge altitude. For example, if the members of an 
extensive system of dune ridges vary in original height from 3 
to 25 feet, with the exception of occasional abnormal individ- 
uals which are manifestly the product of special conditions and 
which may therefore be ignored; and if the average height of 
the older and later ridges is similar, and the building of the entire 
series required 5000 years; then one may safely reject a theory 
which would demand, for example, a continuous progressive 



452 



SHORE RIDGES AND THEIR SIGNIFICANCE 



subsidence averaging 6 inches or a foot per century. For a 
subsidence at the smaller rate for the period mentioned would 
carry the highest of the older ridges down to sealevel and would 
deeply submerge the smaller ones. The fact that there has 
been no material change in the relation of dune crests to sea- 
level between the earlier and later portions of the series is suffi- 
cient indication that there has been no marked change in the 
relative level of land and sea. To admit the possibility of pro- 
gressive subsidence of the land, we would have to assume that 
prograding took place in spite of subsidence, that the earliest 
formed ridges were built 25 feet higher, on an average, than 




Fig. 138. — Beach ridges of equal height separated by swales of different 
depthsTdue to'variations in spacing of ridges. 

the modern ones, and that this excess of height decreased with 
some degree of regularity .and at about the same rate as subsi- 
dence carried the land downward; a series of assumptions diffi- 
cult to grant. 

8. The levels of swale bottoms, whether between beach ridges 
or dune ridges, is of comparatively little significance. This 
follows from the fact that the depth of the swales depends in 
large measure upon the closeness of the spacing of the ridges, 
which is in turn dependent upon factors not usually related to 
changes of level. Figure 138 will serve to make clear the fact 
that a Series of similar ridges of equal height, built on a stable 
shore by a prograding process which varied in rate with varia- 
tions in supply of debris by longshore currents, may be separ- 
ated by swales of very unequal depth. 



RESUME 



We have inquired into the origin of beach ridges and dune 
ridges and have found that while they are produced by waves 
operating under a variety of circumstances, they are not to be 
correlated with individual great storms. Among the* types of 



REFERENCES 453 

current action responsible for the supply of debris built into 
parallel ridges, longshore beach drifting resulting from waves 
breaking obliquely on the shore, although too commonly neglected, 
is believed to be one of the most important. The conditions 
which control the heights of beach and dune ridges have been 
discussed at length, as have also the conditions affecting the rate 
of ridge development. For our guidance in attempting- to esti- 
mate the approximate time represented by any given series of 
beach ridges or dune ridges, certain general principles have been 
laid down; and an examination of the known or estimated rates 
of ridge formation on certain important beach plains has pro- 
vided data which will be of some service in making such attempts. 
Finally, it has been shown that, when interpreted with caution, 
beach and dune ridges may furnish valuable evidence as to past 
changes in the relative level of land and sea; and a series of 
eight fundamental principles, the recognition of which is essen- 
tial to a proper interpretation of such evidence, has been pre- 
sented and discussed. 

REFERENCES 

1. Redman, J. B. The East Coast between the Thames and the Wash 

Estuaries. Min. Proc. Inst. Civ. Eng. XXIII, 186-256, 1864. 

2. Drew, F. [On the Dungeness] quoted by Wm. Topley in "The Geology 

of the Weald." Mem. Geol. Surv. England and Wales, pp. 212-215, 
302-312, 1875. 

3. Redman, J. B. On the Alluvial Formations, and the Local Changes 

of the South Coast of England. Min. Proc. Inst. Civ. Engr. XI, 162- 
204, 1852. 
4 Gulliver, F. P. Dungeness Foreland. Geog. Jour., London. IX, 
536-546, 1897. 

5. Otto, Theodor. Der Darss und Zingst. Jahresb. der Geog. Gesell. 

Greifswald. XIII, 235-485, 1913. 

6. Keilhack, K. Die Verlandung der Swinepforte. Jahrbuch der Konigl. 

Preuss. Geol. Landesanstalt f. 1911. XXXII, 209-244, 1912. 

7. Gilbert, G. K. Lake Bonneville. U. S. Geol. Surv., Mon. I, 47, 55, 

1890. 

8. Ibid., pp. 56-57. 

9. Davis, W. M. Die Erklarende Beschreibung der Landformen, p. 473, 

Leipzig and Berlin, 1912. 

10. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

pp. 708-709, Boston, 1909. 

11. Ibid., pp. 710-715. 

12. Gilbert, G. K. Lake Bonneville. U. S. Geol. Surv., Mon. I, 57, 1890. 

13. Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 

p. 709, Boston, 1909. 



454 SHORE RIDGES AND THEIR SIGNIFICANCE 

Davis, W. M. Die Erklarende Beschreibung der Landformen. P. 473, 
Leipzig and Berlin, 1912. 

14. Redman, J. B. On the Alluvial Formations, and the Local Changes 

of the South Coast of England. Min. Proc. Inst. Civ. Engr. XI, 
~ 162-204, 1852. 

15. Howlett, B. S. [On beach ridges.] Min. Proc. Inst. Civ. Eng. XI, 

213, 1852. 

16. Cubitt, Wm. [On shingle fulls.] Min. Proc. Inst. Civ. Eng. XI, 205, 

1852. 

17. Cornish, Vaughan. On Sea Beaches and Sand Banks. Geog. Jour. 

London. XI, 538, 1898. 

18. Wheeler, W. H. The Sea Coast: Destruction: Littoral Drift: Pro- 

tection, p. 36, London, 1902. 

19. Solger, F. Dunenbuch, pp. 51-52, Stuttgart, 1910. 

20. Keilhack, K. Die Verlandung der Swinepforte. Jahrbuch der Konigl. 

Preuss. Geol. Landesanstalt f. 1911. XXXII, 231, 1912. -~_ 

21. Johnson, Douglas W. and Reed, W. G. The Form of Nantasket 

Beach. Jour, of Geol. XVIII, 188, 1910. 

22. Braun, Gustav. Einige Ergebnisse Entwickelungsgchichtlicher Stu- 

dien an Europaischen Flachlandskusten und ihren Diinen. Zeits. der 
Gesells. fur Erdkunde zu Berlin, pp. 543-560, 1911. 

23. Redman, J. B. On the Alluvial Formations, and the Local Changes 

of the South Coast of England. Min. Proc. Inst. Civ. Engr. XI, 
174, 1852. 

24. Ibid., p. 174. 

25. Drew, F. [On the Dungeness] quoted by Wm. Topley in "The Geology 

of the Weald." Mem! Geol. Surv. England and Wales. P. 309, 1875. 

26. Ibid., p. 214. 

27. Ibid., p. 309. 

28. Gulliver, F. P. Dungeness Foreland. Geogr. Jour., London. IX, 539, 

1897. 

29. Redman, J. B. On the Alluvial Formations, and the Local Changes 

of the South Coast of England. Min. Proc. Inst. Civ. Engr. XI, 
173, 1852. 

30. Gulliver, F. P. Dungeness Foreland. Geog. Jour., London. IX, 539, 

1897. 

31. Lewin, Thomas. The Invasion of Britain by Julius Caesar. 2nd Edi- 

tion, pp. 131 + CXXIV, London, 1862. 

32. Burrows, Montagu. Cinque Ports. 2nd Edition, p. 16, London, 1888. 

33. Drew, F. [On the Dungeness] quoted by Wm. Topley in "The Geology 

of the Weald." Mem. Geol. Surv. England and Wales, p. 308, 1875. 

34. Gulliver, F. P. Dungeness Foreland. Geog. Jour., London. IX, 

539, 1897. 

35. Appach, F. H. Caius Julius Caesar's British Expeditions from Boulogne 

to the Bay of Apuldore, and the Subsequent Formation, Geologically 
of Romney Marsh. 143 pp., London, 1868. 

36. Burrows, Montagu. Cinque Ports. 2nd Edition, p. 16, London, 

1888. 



REFERENCES 455 

37. Robertson, W. A. Scott. The Cinque Port Liberty of Romney. Arch- 

seologica Cantiana. XIII, 261-280, 1880. 

38. Braun, Gustav. Einige Ergebnisse Entwickelungsgeschichtlicher Stu- 

dien an Europaischen Flachlandskiisten und ihren Diinen. Zeits. der 
Gesells. fiir Erdkunde zu Berlin, pp. 546-547, 1911. 
Braun, Gustav. Entwickelungsgeschichtliche Studien an europaischen 
Flachlandskiisten und ihren Diinen. Veroff. Inst fiir Meereskunde 
u. s. w., XV, 14-17, Berlin, 1911. 

39. Otto, Theodor. Der Darss und Zingst. Jahresb. der Geog. Gesells. 

Greifswald. XIII, 235-485, 1913. 

40. Ibid., p. 330. 

41. Ibid., p. 483. 

42. Keilhack, K. Die Verlandung der Swinepforte. Jahrbuch der Konigl, 

Preuss. Geol. Landesanstalt fiir 1911. XXXII, 232, 1912. 

43. Solger, F. Diinenbuch, pp. 46-65, Stuttgart, 1910. 

44. Keilhack, K. Die Verlandung der Swinepforte. Jahrbuch der 

Konigl. Preuss. Geol. Landesanstalt fur 1911. XXXII. 217-218. 225, 
1912. 

45. Ibid., pp. 219, 223, 227. 

46. Otto, Theodor. Der Darss und Zingst. Jahresb. der Geog. Gesells. 

Greifswald. XIII, 337, 1913. 

47. Ibid., p. 484. 

48. Keilhack, K. Die Verlandung der Swinepforte. Jahrbuch der Konigl. 

Preuss. Geol. Landesanstalt fiir 1911. XXXII, 221, 1912. 

49. Ibid., pp. 224-225. 

50. Ibid., p. 231. 

51. Ibid., p. 225. 

52. Kruger, Gustav. Uber Sturmfluten an der Deutschen Kiisten der 

Westlichen Ostsee mit Besonderer Beriicksichtigung der Sturmflut 
vom 30-31 Dezember, 1904. Jahresb. der Geogr. Gesells. zu Greifs- 
wald, 1909-1910. XII, 220-223, 1911. 

53. Keilhack, K. Die Verlandung der Swinepforte. Jahrbuch der Konigl. 

Preuss. Geol. Landesanstalt fiir 1911. XXXII, 227, 1912. 

54. Ibid., p. 217. 

55. Wheeler, W. H. The Sea Coast: Destruction: Littoral Drift: Pro- 

tection, pp. 39, 144, London, 1902. 

56. Goldthwait, J. W. Supposed Evidences of Subsidence of the Coast 

of New Brunswick within Modern Times. Can. Geol. Surv., Museum 
Bulletin No. 2, p. 21 (of reprint) 1914. 

57. Keilhack, K. Die Verlandung der Swinepforte. Jahrbuch der Konigl. 

Preuss. Geol. Landesanstalt fiir 1911. XXXII, 225, 1912. 

58. Sokolow, N. A. Die Diinen: Bildung, Entwickelung und Innerer Bau, 

p. 39, Berlin, 1894. 
Beaurain, G. Quelques Faits Relatifs a la Formation du Littoral des 
Landes de Gascogne Revue de Geog. XXVIII, 255, 1891. 

59. Goldthwait, J. W. Supposed Evidences of Subsidence of the Coast 

of New Brunswick within Modern Time. Can. Geol. Surv., Museum 
Bulletin, No. 2, p. 20 (of reprint), 1914. 



456 SHORE RIDGES AND THEIR SIGNIFICANCE 

60. Cobnish, Vaughan. On Sea Beaches and Sand Banks. Geog. Jour., 

London. XI, 538, 1898. 
fit. Goldthwait, J. W. Supposed Evidences of Subsidence of the Coast of 

New Brunswick within Modern Time. Can. Geol. Surv., Museum 

Bulletin No. 2, pp. 1-23 (of reprint), 1914. 
62. Johnson, Douglas W. and Reed, W. G. The Form of Nantasket 

Beach. Jour, of Geol. XVIII, 162-189, 1910. 



CHAPTER X , 
MINOR SHORE FORMS 

Advance Summary. — There remain for consideration a number 
of shore forms which are not of primary significance in a discus- 
sion of shoreline development, but which are nevertheless of 
much importance to the geographer and geologist, and in some 
cases also to the engineer. It is proposed to give some account 
of these features in the present chapter. Beach cusps are first 
discussed at much length, after which the low and ball, especially 
characteristic of sandy shores, are described. Ripple marks re- 
ceive an extended treatment, following which rill marks, swash 
marks, backwash marks, sand domes, and shore dunes each in 
turn are briefly considered. 

Beach Cusps. — Among the minor forms of the shore zone 
none has proved more puzzling than the cuspate deposits of 
beach material built by wave action along the foreshore. Sand, 
gravel, or coarse cobblestones are heaped together in rather 
uniformly spaced ridges which trend at right angles to the sea 
margin, tapering out to a point near the water's edge. These 
" beach cusps " have attracted the attention of many students, 
and it will be profitable for us to consider first the opinions of 
other writers concerning them; then of examine more carefully 
into their essential characteristics; and finally to criticize the 
various theories which have been proposed to account for their 
origin and development. 

Previous Studies of Beach Cusps. — The earliest account of 
beach cusps which has come to my attention occurs in a paper 
on shingle beaches published by Palmer 1 in 1834. Palmer's 
description of the forms is very vague, but he recognized the 
important fact, not appreciated by all later students, that the 
cusps are produced by waves " driven directly upon the beach," 
whereas they are destroyed when " an oblique direction is given 
to the motion of the waves." In an unpublished thesis, " The 
Geology of Nahant " written by Lane about 1887, the cusps 

457 



458 



MINOR SHORE FORMS 




BEACH CUSPS 459 

on Lynn Beach, Massachusetts, are briefly described and their 
origin discussed. Lane concluded that cusps are formed by 
the action of waves parallel to the coast; that they have their 
beginnings in accidental irregularities on the beach; that they 
become evenly spaced as the result of some process of adjust- 
ment not clearly understood, and that the distance between 
cusps is in some manner related to the height of the waves and 
the breadth of the beach. A short abstract of this thesis was pub- 
lished in 1888, but contains only a brief reference to the cusps 2 . 

A few years later Shaler, in his popular treatise, " Sea and 
Land 3 /' gave a clear description of the curious " ridges and 
furrows " occurring on shores, recognized their temporary char- 
acter and the ease with which they are obliterated by wave 
action, and expressed the opinion that " the origin of these 
peculiar structures is not easily accounted for." Shaler pub- 
lished a somewhat fuller account of beach cusps in his paper on 
" Beaches and Tidal Marshes of the Atlantic Coast." A theory 
of origin was there proposed in the following words: 

" It seems to the writer that these scallops were formed about 
as follows: In a time of storm the inner edge of the swash line 
formed by the body of water which sweeps up and down the 
beach has a very indented front, due to the fact that it is shaped 
by a criss-cross action of many waves. As these tongues run 
up the beach and strike the pebbles, they push them back so 
as to make a slight indentation where each tongue strikes. As 
the water goes back, it pulls out the fine material, but does not 
withdraw the pebbles. The next stroke of the splashing water 
then finds a small bay, the converging horns of which slightly 
heap up the fluid, making the stroke a little harder in the center 
of the tongue and excavating the bottom of the bay still farther. 
As the re-entrant grows larger and the tide rises higher, the water, 
as it runs up, forms a small wave, which breaks on the shore of 
the recess and casts the pebbles more into the form of a ridge. 
This action, continuing for some hours before the tide turns, 
serves to shape the embayment. 

" It should be carefully noted that, when the swaying waters 
rush up into the shore scallops, the converging walls of these 
indentations deepen the current and add to the efficiency of its 
movements — a process which is essentially like that which is 
brought about when an ordinary wave enters into a recess of the 



460 MINOR SHORE FORMS 

cliff, or the tidal undulation is crowded into an indentation 
such as the Bay of Fundy 4 ." 

In his paper on " Sea-beaches and Sand-banks " published in 
1898, Cornish briefly refers to the " succession of ridge and 
furrow at right angles to the sea-front," and attributes the 
phenomenon to the erosive action of waves which are increasing 
in size and attempting to reduce the beach slope to a gentler 
gradient. A variation of the same feature is described by 
Cornish under the name " Shingle Barchanes." He was of the 
opinion that the shingle barchanes were analogous to that form 
of sand dune called a barchane, and considered any discussion 
of their origin superfluous 5 . 

One year later Jefferson published a paper in which he de- 
scribed some of the characteristic features of beach cusps and 
offered an explanation of their origin. Jefferson's studies were 
" made at a single beach (Lynn Beach, Massachusetts), though 
confirmed by some observations from Gay Head and Narragan- 
sett Bay." He concluded that the cusps were caused by the 
escape of water from behind a barrier of seaweed located near 
the upper zone of the beach. Occasional waves of more than 
average size overtop the seaweed barrier and leave large quan- 
tities of water imprisoned behind it. After the retreat of the 
wave the imprisoned water escapes through occasional breaches 
in the barrier and flows down the beach in streams of consider- 
able strength, which scour away the beach material along their 
courses. The residual masses of material thus left between the 
stream lines are gradually shaped by the waves into typical 
beach cusps. A stony barrier would probably not operate in 
the same manner as a barrier of seaweed, since the water would 
filter through the mass rather than wear channels. " It would 
seem to follow that such stony cusps are to be looked for only 
on coasts where seaweed or some similar material is abundantly 
thrown up 6 ." 

In 1900 Branner published a paper entitled " The Origin of 
Beach Cusps," based on observations made on the California 
coast and the northeast coast of Brazil. He noted the fact that 
cusps occur where ." there are no seaweeds or other ' drift ' on 
the beach," and concluded that they are formed " by the inter- 
ference of two sets of waves of translation upon the beach." 
The accompanying diagrams, reproduced from Branner's paper, 



BEACH CUSPS 



461 



will serve to make his theory clear. In Figure 139 " the concen- 
tric lines represent two sets of waves advancing on the beach in 
the direction indicated by the arrows and crossing each other along 
the broken lines. In deep water these are waves of oscillation, 
but when they reach the shallow water on the beach they become 
waves of translation and interfere with each other where they 
converge upon the shore. The tendency is for them to check 




Fib. 139. — Diagram illustrating Branner's theory of beach cusp formation. 



It each 


Beciffb\ 


\ ' / ' \ 1 S l\ ' 

/A^'/A / X 

' \r i \!/ i \ 
J A / X / \ 


ggy%^ 


^ffiS 


''/TV/A/ \/v\X \\\ \ 



Fig. 140. — Diagram illustrating Branner's theory of the formation of un- 
equally spaced beach cusps. If DC were the beach, the cusps would be 
uniformly spaced. 

each other along these lines of interference and to heap up the 
sands at the points marked A, where they strike the beach. 
At the points marked B the waves diverge and throw the beach 
sands and all floating material alternately right and left." 

" In Figure 140 the waves are represented as breaking on a 
straight beach. If the water offshore were of a uniform depth 
and the waves were evenly spaced, the cusps in this case would, 
for obvious reasons, be farther and farther apart from left to 



462 MINOR SHORE FORMS 

right, as shown along the beach DE. The distance between 
the cusps is equal to the spaces measured on the beach between 
the radii along which the wave interference approaches the 
shore 7 ." In an editorial note in the Journal of Geology for 
1901, Branner briefly restated his theory of cusp formation, and 
called attention to the fact that " giant ripples " and similar 
beach structures observed in sedimentary rocks may be fossil 
beach cusps 8 . 

Among the " Author's abstracts of papers read at the Wash- 
ington meeting of the American Association for the Advance- 
ment of Science, Section E," published in the Journal of Geology 
for 1903, is an abstract of a paper by Jefferson entitled " Shore 
Phenomena on Lake Huron." The abstract suggests a modi- 
fication of the author's views as published four years before; 
for while in the earlier paper the possibility of a stony barrier's 
playing the same part in cusp formation as a seaweed barrier is 
considered and rejected as improbable, in the later paper we 
read that the cusps are " component features of a beach ridge, . . . 
The ridge . . . has at times been seen and photographed with 
water caught behind and rushing out at breaks in the line, as 
with the weed line at Lynn 9 ." Whether or not the breaking 
of water through the barrier is still thought to originate the 
cusps is not made clear. The cross-waves noted by Branner 
were observed by Jefferson, but at no place did he find such 
waves associated with cusp formation. 

Alexander Agassiz in a report on " The Coral Reefs of the 
Tropical Pacific 10 ," figures a series of " boulder cusps " observed 
on the shores of Arhno atoll. Judging from the illustration 
these are true beach cusps; but the method of origin advocated 
by Agassiz is that described on an earlier page of the present 
volume for the formation of cobblestone deltas in marshes or 
lagoons by waves washing over a low beach. The position of 
the " boulder cusps " on the shores of a narrow lagoon, is com- 
patible with the delta theory rather than with the beach cusp 
theory; but the forms as figured could not have been produced 
by over washing waves. Some doubt must therefore attach to 
Agassiz's brief observations. 

In his paper " Cuspate Forelands along the Bay of Quinte " ll 
A. W. G. Wilson describes the occurrence of " cusplefs " on 
one of the forelands, and ascribes them to the action of a single 



BEACH CUSPS 463 

series of waves striking the beach at an oblique angle. Although 
Wilson does not refer to the previously published accounts, and 
although the very asymmetrical forms described by him differ 
in some respects from the essentially symmetrical features gen- 
erally known as beach cusps, there is little reason to doubt 
that the former are modified phases of the latter. 

In 1905 Jefferson published a paper entitled " On the Lake 
Shore" 12 , in which he gives a brief account of beach cusps, 
and says " they never occur except after waves that have played 
squarely on shore." Examples which must have formed with- 
out the aid of seaweed barrier are figured, but their origin is 
not explained. In referring to one particular set, however, 
Jefferson classes them with the Lynn beach cusps, and says: 
" Some high wave surmounts the ridge, here of sand, there of 
seaweed, and its crest water is ponded behind it to escape by any 
sags that may occur in the line." 

My own attention was first directed to the study of beach 
cusps in the fall of 1903. Seven years later I discussed their 
form and origin in a paper published in the Bulletin of the Geo- 
logical Society of America 13 , and it is upon this paper that the 
present discussion of beach cusps is largely based. 

Characteristics of Beach Cusps. — When most perfectly de- 
veloped, the ideal beach cusp has a shape suggesting an isosceles 
triangle, and is so placed that the unequal side (hereafter called 
the base) is parallel to, but farthest from, the shoreline. The 
" triangle " may be short and blunt, or may be so greatly elon- 
gated that the two equal sides extend far down the beach and 
finally unite to form an acute point (hereafter called the apex). 
These same sides may be relatively straight, but are more often 
concave, sometimes convex, outward. The actual variations in 
form are numerous and wide (Fig. 141). Every gradation can 
be found from well developed triangular accumulations of sand 
or gravel to widely spaced heaps of cobblestones of no definite 
shape. The cusps may constitute the serrate seaward side of a 
prominent beach ridge, or may occur as isolated gravel hillocks 
separated by fairly uniform spaces of smooth sandy beach. 
They may be sharply differentiated from the. rest of the beach, 
or may occur as gentle undulations of the same material as the 
beach proper, and so be scarcely discernible as independent 
features. Indeed, the variations in beach cusps are so great 



464 



MINOR SHORE FORMS 



I 




* 





% 



- 



BEACH CUSPS 



465 



that their form is often not as sure a guide to their detection as 
is their systematic recurrence at fairly uniform intervals. One 
or two indefinite heaps of gravel on a beach would escape notice, 
but a hundred such heaps, evenly spaced, attract attention. 

A cusp may rise from an inch or less to several feet above 
the general level of the beach. Many are relatively low and 



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Fig. 141. — Variations in the form of beach cusps. 



flat, others high and steep-sided. Sometimes the highest part 
is comparatively near the apex; at other times the highest 
part is far back, and from it a long, sloping ridge trails forward 
toward the water. As a rule, the cusps appear to point straight 
out toward the water, and neither side of a cusp is steeper than 
the other except where oblique, wind-made waves have eroded 
one side only, a condition observed in a few cases. 

An interesting variation in form is found where old cusps ter- 
minate abruptly in little " cliffs " instead of in sharp points 
(Plate LVI). It is plain that after the old cusps had been 
formed they were cliffed by waves under changed conditions and 
their apices cut away. From this eroded material later series of 
cusps may form, unrelated in position to the original series. Fig- 
ure 142 represents a case of this kind as observed in cobblestone 



466 MINOR SHORE FORMS 

and gravel cusps on a gravel beach at Winthrop, Massachusetts. 
Sometimes the cusps are more completely eroded than in the 
case figured, and remnants of three or four distinct sets, of differ- 
ent sizes and spacing, may often be observed on a beach at one 
time. 

As in the form of cusps, so in the material of which they are 




Fig. 142. — Partially eroded older cusps and respaced later series. 

composed, is there the widest variation. In building them the 
waves make use of everything, from the finest sand to the 
coarsest cobblestones. There is no necessary relation between 
the size of the cusp and the size of the material of which it is 
composed. Large cusps built wholly of fine sand are reported 
from Virginia Beach, and still larger ones (20 to 30 feet from 
apex to base and 75 to 90 feet between apices) built of similar 
material were observed on the beach south of Dyker Heights 
on Long Island. Kemp 14 has studied large sand cusps on Mel- 
bourne Beach, Florida, which measured from 90 to 95 feet 
between apices and rose at least 3 or 4 feet above the general 
level of the beach. The largest examples are more often built 
of coarse gravel or cobblestones, while small ones may be com- 
posed of either fine sand or coarse gravel. The very smallest 
cusps, measuring a few inches in length, consist of fine material 
only, since the small waves which build them cannot transport 
coarse gravel or cobblestones. Where both coarse and fine 
materials occur on a beach, the cusps are built of the coarse 
material. Gravel cusps on a sandy beach are of common occur- 
ence, but I have not observed sand cusps on a gravel beach. 
The smallest cusps which have come under my observation 



BEACH CUSPS 467 

have been those artificially produced in the laboratory. These 
have varied from an inch to several inches in length, measured 
from apex to base. Some almost as small are to be found along 
the shores of sheltered ponds. On a sandy beach at the head 
of a protected bay south of Huletts Landing, Lake George, 
cusps from 8 to 12 inches long were formed by the small waves 
set in motion by a gentle breeze. Those found along the sea- 
shore may reach a length of 30 feet or more. It should be 
noted, however, that the length measured from apex to base is 
less significant than the distance between cusps, measured from 
apex to apex; for while it is a general rule that the farther 
apart the cusps the larger is their size, some which are closely 
spaced may be greatly elongated, as pointed out above, and this 
elongation appears to be the result of rather accidental condi- 
tions, and to have no great significance. Measurements across 
the bases might be more significant, but it is often difficult to 
determine the length of base, as when the cusps form part of 
a beach ridge or constitute widely separated heaps of gravel 
having a vague shoreward boundary. However, enough has 
been said to give some idea of the range in size; and although 
size is in some degree related to spacing, the latter is the really 
important factor, as noted below. 

The very small cusps made in the laboratory are from one to 
several inches apart, measured from apex to apex. On the shore 
of small ponds and bays, where only small waves are developed, 
the spacing varies from less than a foot to two feet or more. 
On sea beaches the cusps built by small waves may be less than 
10 feet apart, while those built by large storm waves may be 
100 feet apart. 

Jefferson emphasizes the lack of regularity in the spacing of 
cusps, whereas others have been impressed by their regular 
recurrence at fairly uniform intervals. Inasmuch as the matter 
of spacing is of vital importance in any discussion of the origin 
of these forms, we may examine it somewhat carefully. Jeffer- 
son 15 writes: " The constant recurrence of bay (inter cusp space) 
and point (apex) as one walks along the beach suggests that 
there is a regularity in the width of intervals. This is not so, 
however, on Lynn Beach, as appears from the diagram, meas- 
ures from point to point along the beach being 21, 20, 18, 16, 22, 
17, 6, 7, and 22 paces. Fainter cusps farther south toward 



468 



MINOR SHORE FORMS 




PQ 



BEACH CUSPS 469 

Nahant show similar irregularity. It might be said, however, 
that on Lynn Beach they are commonly about 20 paces wide." 
And again 16 : "In a view along the beach these unevennesses 
are foreshortened into the appearance of points of sand or gravel 
known as beach cusps. They are less even than they look." 
In still another connection he says: " Perspective foreshortening 
gives them a fictitious appearance of regularity 17 ." On the 
other hand, Shaler 18 speaks of their " orderly and uniform suc- 
cession"; and it has seemed to me that the degree of regu- 
larity in spacing is so great as to be incompatible with certain 
of the proposed theories of origin. 

It is true that measurements of the spaces do not always give 
exactly the same figure; that in the early stages of development 
a greater degree of irregularity prevails than later on; and that 
even where cusps are very perfectly developed, occasional aber- 
rant features obscure the regularity of spacing. Nevertheless, 
a large number of observations of beach cusps in all stages of 
formation and destruction, and the production of artificial cusps 
in the laboratory have convinced me that a fairly high degree of 
regularity in spacing is a most characteristic feature of well 
developed forms and must carefully be considered in any attempt 
to account for their origin. 

The width of the intercusp spaces varies with the size of the 
waves. When the waves are about an inch in height the cusps 
are from 3 to 9 inches apart; when the waves are from one and 
a half to two and a half feet high they are 30 to 60 feet apart , 
while large storm waves build cusps 100 feet or more apart. 
These figures are only approximate, and are based on rough 
estimates of the wave height close to the shoreline. Sufficient 
data have not been secured on which to base a reliable deter- 
mination of the precise relation of intercusp space to wave 
height, but within certain limits there is a suggestion that 
doubling the v/ave height doubles the length of the space. A 
large number of careful observations would probably establish 
this point. In conducting such an investigation the observer 
must satisfy himself that the waves he sees are actually building 
the cusps, for waves of any size may play about cusps formed 
by other waves of different size, and thus mislead one who 
compares the intercusp spaces with the height of the later 
waves. Fortunately a given set of waves does not long leave 



470 MINOR SHORE FORMS 

unmolested a series of cusps formed by waves of an entirely 
different size, and the patient observer can in time determine 
whether or not the waves then breaking on the beach are to be 
correlated with the cusps at the water's edge. 

This brings us to the consideration of another significant 
point in connection with the spacing of beach cusps: namely, 
the relative ease with which old cusps are remodeled by waves 
differing in size from those which formed them. If closely 
spaced cusps formed by small waves are attacked by larger 
waves, there ensues a rearrangement by which the cusps become 
larger and farther apart. This rearrangement may be gradual, 
and may be accompanied by the combining of some cusps and 
the slow obliteration of others; or if the new waves are very 
large, there may be a rapid obliteration of the earlier series of 
cusps, followed by the slow formation of a new series adjusted 
to the size of the later waves. If the widely spaced cusps formed 
by large waves are attacked by smaller waves, so much of the 
older cusps as can be reached will be eroded and the material 
refashioned into smaller cusps more closely spaced, regardless 
of the positions of the older ones (Fig. 142). When large and 
widely spaced cusps are built by high storm waves well up the 
slope of the beach, only their apices are apt to be attacked by 
the smaller waves of calmer weather, and so it happens that we 
commonly find the largest cusps partially preserved near the 
top of the beach, with series of smaller and more closely spaced 
cusps farther down the slope. 

Regarding the building of beach cusps, Jefferson 19 writes: 
"If it be asked how this begins, the answer must be that the 
beginning is as old as the beach. . . . Each set of cusps 
may modify its successors. A new crest of seaweed flung up 
today is likely to have its weak points in some measure deter- 
mined by the previous channels. In violent storms it is doubtful 
if this control is significant. Each storm probably sets the 
shape in which the waves must play for a long time." If we 
accept Jefferson's theory of cusp formation, the conclusions just 
quoted would seem to be reasonable. But the sensitiveness of 
beach cusps to changes in size of waves leads to quite opposite 
conclusions. Instead of the beginning of cusp formation dating 
back indefinitely, there appears to be a new and quite inde- 
pendent beginning with every marked change in the size of 



BEACH CUSPS 471 

waves. One set of cusps seems to have little influence on the 
position of its successors. Along the shores of a little bay just 
south of Huletts Landing, Lake George, cusps built by small 
waves are completely obliterated each day by three or four of 
the large waves which strike the beach after the passing of a 
steamboat. Opposite the cusps, but farther up the beach, pegs 
were driven to mark the position of the cusps. After their 
obliteration they formed again under the influence of the small 
waves, with the same size and spacing as before, but, as shown 
by the pegs, in totally new positions. The law controlling the 
relation of spacing to wave size was operative, but the cusps 
which were there a few moments before did not determine the 
position of their successors. The same phenomenon may be 
observed in the production of artificial cusps. Furthermore, if 
a series of parallel trenches be excavated in the artificial beach 
at right angles to the shoreline, the intercusp spaces and the 
cusps will not correspond with the trenches and intervening 
ridges which have been made to guide wave action. In fact, 
waves of a given size insist on forming cusps at appropriate 
intervals, and while their action may be influenced within cer- 
tain limits by natural or artificial trenches on the beach, they 
refuse to be controlled by such depressions unless these are 
themselves appropriately spaced. Kemp 20 reports that at Mel- 
bourne Beach on the Florida coast continuous observations 
throughout one winter show that the cusps of one day may be 
completely obliterated in a few hours, and the beach left feature- 
less and smooth. The next series of waves will form a new series 
of cusps quite unrelated in spacing to the earlier series. 

The bases of the cusps often merge with the last formed 
beach ridge in such a manner as to leave no doubt that they 
constitute an integral part of it. The ridge may or may not be 
breached opposite the intercusp spaces; but it should be noted 
that with the progressive concentration of the water in the 
intercusp spaces, which converge shoreward, the parts of the 
ridge most likely to be broken through are the parts opposite 
these spaces. It is, therefore, not necessary to regard the in- 
tercusp spaces as the product of erosion by water which was 
imprisoned back of the ridge and broke through it, either at 
the lowest places or at points of weakness. Conclusive evidence 
that the ridge may be breached from the seaward side is found 



472 



MINOR SHORE FORMS 







BEACH CUSPS 473 

in the gravel or cobblestone deltas which are sometimes built 
landward from the gap in a ridge at the head of an intercuop 
space (Fig. 143). It seems clear that the water concentrated 
between cusps broke through the ridge and carried gravel and 
cobbles into the area back of it. In one case observed at Nahant 
the landward projection of cobblestone accumulations was so 
systematic as to give a series of " inverted cusps " alternating 



•■„■ " #vVv*:Xn« i .* '• .*.*••*•*. V.- • 
. SJl3S^±ine 




n "1/ ' — . _ — ; — =-_" - — ~ ~~ ~ _ 


f~-"l-7-~F-^-^" 



Fig. 143. — Normal and inverted beach cusps. 

regularly with the beach cusps proper. The breaching of the 
ridge by water concentrated between previously formed cusps 
has been repeatedly observed in the laboratory experiments. 

There are abundant instances of cusps unrelated to any beach 
ridge. Cusps of gravel are often formed at widely separated 
intervals with smooth, sandy beach between; the points of old 
cusps are nipped off and respaced without the development of a 
ridge. One must conclude that cusps may develop as the ser- 
rate seaward margin of a beach ridge and may determine the 
places where it will be breached by the waves, but that there is 
no necessary relation between the two. 

The return current of water flowing down the beach after 
the wave has ended its advance, sweeps seaward more or less 
fine material which is deposited to form the shoreface terrace. 
When cusps have not formed, the margin of this terrace is rela- 
tively straight; but after cusps have developed, the greatest 



474 MINOR SHORE FORMS 

amount of water and debris returns down the slope from the 
intercusp spaces, building the subaqueous platform seaward 
more rapidly than does the smaller amount of water and debris 
returning from around the apices of the cusps. In this way the 
margin of the platform becomes scalloped, each intercusp space 
having a scallop or miniature delta to correspond with it. It is 
evident that the scalloping of the platform presents no difficulty 
if the origin of the cusps is understood. 

Relation of Beach Cusps to other Factors of Shore Activity. — ■ 
In collecting data concerning beach cusps some attention has 
been given to several other factors of shore activity, in view 
of the possibility that they might exert some influence on 
cusp formation. Several of these factors are briefly treated 
below. 

It was thought at first that the angle of beach slope might 
exert an important control over the spacing of the cusps, inas- 
much as the slope affects both the volume and velocity of the 
water advancing and retreating over the zone of wave attack. 
It soon became apparent, however, that if the inclination of the 
beach does influence the spacing, the effect is largely masked by 
the far more important factor of wave size. I still think it 
probable that the slope of the beach plays a small part in the 
spacing of cusps, but have not sufficient data on this point to 
demonstrate the truth of the theory. 

The direction of the wind seems to have little effect on the 
formation of cusps. They have been observed in process of 
formation during onshore, offshore, and longshore winds, both 
gentle and fairly strong. Under ordinary conditions the only 
result noticed was a more or less marked cliffing on one side of 
the cusps when the wind produced small waves at an angle 
oblique to the beach. The cusps thus cliffed may have been 
partially developed before the oblique waves began their work. 
If the wind is strong enough and from such a direction as to 
combine with the breakers in producing a very irregular wave 
attack, the formation of cusps is probably interferred with, since 
numerous observations tend to show that a fairly regular ad- 
vance and retreat of the water is essential to their development. 

Beach cusps are formed at all stages of the tide. It is prob- 
able that the greatly elongated type is produced when the waves 
remain of approximately the same size during a falling tide, but 



BEACH CUSPS 475 

the development of this type has not been observed throughout 
the entire process. 

The direction of wave advance has been carefully noted where- 
ever cusps were being formed. On the basis of numerous ob- 
servations on all kinds of beaches and of extended experimenta- 
tion, it may be confidently stated that the best conditions for 
cusp formation exist when a single series of waves advances 
parallel with the beach. It is possible that cusps may be pro- 
duced by waves striking the shore at a markedly oblique angle, 
but no satisfactory evidence that such is the case has been 
secured. On the other hand, the progressive destruction of 
cusps by oblique waves has been repeatedly observed. Such 
partially destroyed forms are shown in the lower left-hand corner 
of Figure 141. I am inclined to think that the asymmetrical 
" cusplets " reported by Wilson 21 were formerly symmetrical 
beach cusps of the ordinary type, which were later cliffed by the 
oblique waves shown in a photograph reproduced in his paper. 
Intersecting waves of the type appealed to by Branner have 
been seen in a number of cases, but no cusps have been observed 
to develop under the action of such waves. 

The periodicity of the waves does not appear to be a signifi- 
cant factor in beach cusp formation. Varying the period with 
artificial waves produces no apparent effect on the cusps. 

Jefferson 22 says: " The cusps seem related to a longshore 
current, their precise cause not being evident"; but he does 
not indicate in what manner the cusps seemed related to the 
current. In most of my observations no evidence of a long- 
shore movement of the water was found. In the few cases 
where a distinct drift or current in one direction was apparent 
there seemed to be no relation between the current and the 
cusps. Beach cusps seem clearly to be the product of on- and 
offshore movements of the water.. 

Artificial Beach Cusps. — From the observation of natural 
beach cusps in process of formation the conclusion was reached 
that cusps could be formed by a single series of waves advanc- 
ing parallel with the shore. In order to test the validity of this 
conclusion the artificial production of cusps was attempted. A 
sand beach was constructed along one side of a tank 5 feet square 
and the water in the tank raised until it rested against the 
beach slope. To make that slope as smooth and gentle as 



476 



MINOR SHORE FORMS 



possible, large waves were washed over the beach until it ap- 
peared to the eye as a perfectly uniform, gentle slope of sand. 
On the opposite side of the tank from the beach was arranged 
the wave-producing apparatus. This consisted at first of a 
board which was tipped up and down by hand; later of two 
boards hinged together, one of which was made stationary on 
the floor of the tank, while the other could be raised and lowered 
by a long handle connecting with its free edge. With this 
simple apparatus it was possible to propel on the beach a series 
of parallel, straight waves, varying in size and periodicity as 
the experimenter desired. It was found that beach cusps re- 
sembling closely those in 
nature could be artificially 
produced (Fig. 144). The 
characteristic features of 
these artificial cusps have 
been discussed above. 

Theories of Origin. — ■ 
With the characteristics 
of beach cusps in mind, 
we may critically examine 
the theories which have 
been proposed to account 
for their origin. 

The unpublished manu- 
script of 1887, in which 
Lane discusses the characteristics of beach cusps, does not set forth 
a complete theory of their origin, but does contain exceptionally 
good observations on the more significant features of their 
occurrence. It will presently appear that some of the signifi- 
cant relationships noted by Lane, and quoted on an earlier page, 
are necessarily involved in the theory of origin advanced by the 
present writer. 

According to Shaler, " the inner edge of the swash line . . . 
has a very indented front, due to the fact that it is shaped by 
a criss-cross action of many different waves 32 ." The projecting 
tongues of water .push back the pebbles, leaving indentations 
or bays, which are then enlarged under the continued wave 
attack during the rising tide. It should be noted, however, 
that the indentations of the inner edge of the swash line on a 




Fig. 144. — Artiticiai beach cusps. 



BEACH CUSPS 477 

smooth beach are extremely irregular, and vary in position with 
every wave advance until the development of cusps and inter- 
cusp depressions affords more definite guidance. That a single 
advance of the irregular inner edge of the swash could develop 
bays which would thereafter control the action of the waves 
seems doubtful. The inner edge of the swash is thin as well as 
irregular and variable, and under these conditions must be very 
ineffective in developing intercusp spaces or " bays." Nor does 
the theory as stated by its author explain the regularity in spac- 
ing of the cusps nor their respacing consequent upon a change 
in size of waves. It would seem that Shaler's theory does not 
go far enough adequately to explain the observed phenomena. 

In the account of " ridges and furrows " (cusps and intercusp 
spaces) given by Cornish 24 it is stated that the water washes 
depressions at selected places because neither the force of the 
water nor the resistance of the beach material to erosion is 
absolutely uniform. The regular spacing of the cusps is not 
explained, nor does the author appear to have recognized this 
character of their distribution. Neither does he recognize the 
fact that gentle waves build cusps. The erosion which pro- 
duces the " furrowing " is related by him to a change from 
small to large waves only. But we have seen that cusps form 
under reverse conditions as well. It thus appears that Cornish 
points out certain causes of the unequal erosion of beaches, but 
does not throw much light upon the origin of the cusps. 

The seaweed barrier theory of Jefferson 25 advanced to account 
for the occurrence of cusps on a beach where there happened 
to be considerable accumulations of seaweed at the time, breaks 
down under the test of a broader application. There are also 
serious objections to the theory aside from the fact that cusps 
are abundantly developed on beaches free from seaweed and 
other similar material. Even if we admit that a strip of sea- 
weed might form an effective dam behind which considerable 
masses of water would be imprisoned, we must regard it as in 
the highest degree improbable that this water would break 
through the seaweed barrier at a large number of rather evenly 
and often closely spaced intervals. The degree of regularity 
in beach cusp spacing is wholly incompatible with the seaweed 
barrier theory. 

On the other hand it should be remembered that after the 



478 MINOR SHORE FORMS 

cusps have once formed, a seaweed barrier, as well as a barrier 
of sand or gravel, may be breached by the waves where their 
water is concentrated for the attack in the intercusp spaces. 
Thus an observer might find breaches in the barrier correspond- 
ing with the intercusp spaces. As shown more fully on a pre- 
ceding page, both theoretical considerations and the field evi- 
dence support the view that the breaching is effected by direct 
wave attack, and not by the escape of water imprisoned behind 
the barrier. There is good ground for the belief that the breach- 
ing of the seaweed barrier on Lynn Beach was the effect instead 
of the cause of cusp formation. 

In Jefferson's more recent accounts 26 the question of origin 
is very briefly referred to; but from such reference it appears 
that the author later considered a barrier of sand or gravel 
capable of playing the same role in cusp formation as a seaweed 
barrier. It is further implied that other cusps must have had 
a different but unknown origin. The objections urged against 
the seaweed barrier theory apply, in the main, with equal force 
against the sand or gravel barrier theory. It is true that ridges 
of sand and gravel are more frequent on beaches than barriers 
of seaweed ; but the evidence is conclusive that cusps are formed 
when such ridges are absent, and that even when present such 
ridges are breached from the seaward side by direct wave attack, 
and not from the landward side by impounded waters. 

On both natural and artificial beaches more or less distinct 
ridges are sometimes broken through before any distinct cusps 
have been formed. This led me to entertain the hypothesis 
that direct wave attack on a fairly uniform ridge would develop 
breaches in the ridge at intervals proportional to the size of the 
waves. It seems probable, however, that faint undulations in 
the beach, on the seaward side of the ridge, may help to deter- 
mine the points of breaking just as the more evident cusps and 
intercusp spaces do in other cases, and that the breached ridges 
are therefore but one phase, and not an essential one, of the 
process of cusp formation, as explained on a later page. 

Branner's theory 27 , while very suggestive, seems to present 
insuperable obstacles, as will be apparent on the inspection of 
his diagrams (Figs. 139 and 140). The hypothetical wave lines 
are evenly spaced, and the wave length in both sets is the 
same. This is a condition which probably never obtains in 



BEACH CUSPS 479 

nature, and yet such an improbable condition is an essential 
element of the theory. If the two sets of waves are given 
different wave lengths, or if one set of waves has a velocity 
differing from that of the other, or if either set of waves is irregu- 
larly spaced, then the points of wave interference will not reach 
the beach at the same place twice in succession. If we endeavor 
to approximate natural conditions by introducing any one of 
the three types of irregularities mentioned (and probably all 
three exist in every case of intersecting waves), we must correct 
the diagrams by making the dotted lines meet the shoreline at 
every conceivable point. This done, the supposed reason for 
cusp formation disappears. 

It has been shown on preceding pages that the physical con- 
ditions necessary for cusp formation exist in parallel waves. 
One might accordingly surmise that in intersecting waves the 
necessary equilibrium would be destroyed and the formation of 
cusps rendered more difficult, or even impossible. I believe 
this to be the case. In 1907, while camping near Huletts 
Landing, opportunity was afforded to make numerous obser- 
vations during a period of six weeks, on a portion of the lake 
shore where intersecting waves were usually developed by a 
sand and gravel bar offshore. At no time were cusps observed 
on the portion of the beach where intersecting waves arrived, 
although they were frequently found on adjacent portions. 
These observations led to the belief that intersecting waves 
tend to prevent rather than to cause the formation of beach 
cusps. 

Inasmuch as the " cusplets " described by Wilson 28 appear 
to be true beach cusps of somewhat unusual form, it is proper 
to consider the hypothesis offered to account for their origin. 
According to this author, evenly spaced waves striking a straight 
shoreline at an oblique angle will give evenly spaced points of 
wave-breaking at which cusps will develop. Because at any 
given instant a series of oblique waves will be breaking at a 
number of different points along a beach, the author assumes 
that the points of simultaneous wave-breaking will be nodal 
points where material will tend to accumulate. It would 
appear that no account is taken of the fact that every oblique 
wave of the series breaks not only at the point observed during 
a given instant, but also at all the other points up and down the 



480 MINOR SHORE FORMS 

beach, so long as the wave exists. The point of breaking of an 
oblique wave sweeps along the shore until the end of the wave 
itself is reached. In a series of waves parallel to each other, 
but oblique to the shoreline, each wave in turn breaks continu- 
ously from one end of the beach to the other. Under these 
conditions no nodal points can develop, and the fact that the 
waves are a given distance apart, and that at any given instant 
their points of contact with the shore are evenly spaced, is 
immaterial so far as the distribution of force of wave attack is 
concerned. 

In addition to the theoretical objections to Wilson's theory 
must be added the observed fact that oblique waves appear to 
be much less favorable to cusp formation than are waves parallel 
to the shoreline. Oblique waves have been observed in the 
process of cliffing the sides of cusps exposed to their attack, 
and the remains of the cusps then have the asymmetrical form 
decribed by this author. 

In attempting to explain the formation of beach cusps I have 
tested and rejected several working hypotheses in addition to 
those mentioned above. For example, there was considered the 
possibility that the waves breaking parallel with the shore had 
superposed obliquely upon them smaller waves, and that the 
portions of the main waves thus increased in height excavated 
the intercusp spaces. One bit of evidence which appeared to 
harmonize with this theory was personally reported to me by 
Mr. T. I. Read, who noted that on Virginia Beach the incoming 
waves showed the first tendency to break at regularly spaced 
intervals which corresponded with the intervals between cusps. 
The hypothesis was rejected because the cause was irregular, 
while the effect was regular; because of an almost complete 
lack of direct evidence pointing to a relation between superposed 
waves and cusps; and because experiments seemed to point 
conclusively to some other origin. 

Another hypothesis was based on the assumption that an 
extended sheet of water descending an inclined plane may not 
move with the same velocity throughout, but may tend to de- 
velop lines of swifter flow, or currents, at certain intervals. I 
was tempted to make this assumption because of the fact that 
water descending a flat-bottomed inclined trough, or conduit, 
does not flow uniformly, but is successively retarded in such a 



BEACH CUSPS 481 

manner as to produce a succession of waves. Admirable illus- 
trations of this phenomenon have been published by Cornish 29 
in a paper on " Progressive Waves in Rivers." It occurred to 
me that if a broader sheet of fluid were retarded by friction 
while descending an inclined plane, the resistance might be 
overcome first, or more rapidly, at certain points, and that the 
slightly increased rate of advance at these points would disturb 
the equilibrium in such manner as to create zones or currents 
of accelerated flow wherever these slight initial advantages had 
been gained. If the sheet of water were shallow, there would 
be a tendency for the currents to be smaller and more closely 
spaced than if the sheet of water were of greater depth. This 
hypothesis was especially tempting, inasmuch as granting the 
basal assumption all the phenomena of beach cusps find a 
ready explanation. Small waves advancing and retreating on 
the beach would give small currents closely spaced, which would 
in turn scour small intercusp spaces leaving closely spaced cusps. 
Any change in the size of waves resulting in a change in the size 
and spacing of the currents would necessitate a respacing of 
the cusps. The hypothesis does not lack support so far as the 
phenomena of beach cusps are concerned, but it is based on an 
assumption which does lack support. I have questioned a num- 
ber of engineers and physicists in regard to the matter, but 
could learn nothing favorable to the assumption. 

The hypothesis which best accords with all of the available 
evidence may now be set forth. Concisely stated, it is that 
selective erosion by the swash develops from initial irregular 
depressions in the beach shallow troughs of approximately uni- 
form breadth, whose ultimate size is proportional to the size 
of the waves, and determines the relatively uniform spacing 
of the cusps which develop on the inter-trough elevations. This 
theory differs essentially from those proposed by Branner and 
Wilson in that neither intersecting nor oblique waves are ap- 
pealed to and the spacing of the waves is disregarded; from 
those proposed by Jefferson and Cornish in that the cusps are 
not regarded as mere erosion remnants of a once continuous 
ridge, while uniformity of spacing depending on wave size is 
considered of vital importance; from the theory proposed by 
Shaler in that no importance is attached to the irregular front 
of the swash, the ability of the thin edge of the swash to develop 



482 MINOR SHORE FORMS 

the intercusp bays is not admitted, while the size of the wave 
is correlated with the width of intercusp spaces. Other points 
of difference will appear in the explanation which follows. 

Every beach contains numerous inequalities which tend to 
prevent a uniform flow of water up and down the beach during 
wave action. These inequalities have a variety of causes. Sur- 
face run-off after rains may develop channels on the beach; the 
water draining out of the sand at the upper part of the beach 
after high tides or after high waves may produce the same 
result. Pebbles lying on a sandy beach interfere with the 
swash of water up and down the beach, and cause some channel- 
ing. The waves are never even-crested, and may be very irreg- 
ular if oblique waves are superposed on them; the irregularity 
of the swash line, mentioned by Shaler, may initiate irregu- 
larities on the beach. Remnants of old beach cusps, not wholly 
obliterated, form another source of irregularity; and still other 
sources might be mentioned. 

The continual swashing of the water up and down the beach 
tends to enlarge the irregular depressions over which the water 
passes. Larger channels are better adapted to the movements 
of the large volumes of wave-supplied water. It is inevitable 
that in the enlarging of some depressions others will be obliter- 
ated, just as in the case of growing drainage basins many small 
basins disappear as independent features, while the few increase 
in size. Those depressions on the beach which develop to larger 
proportions will be the ones which have some initial accidental 
advantage, and which increase that advantage as they grow; 
just as the accidental^ favored drainage basins increase in 
size and advantage at the expense of those which began the 
contest with but a slightly less favorable chance. The tendency 
of wave action will be to develop from initial irregularities a 
smaller number of broad and shallow depressions on that por- 
tion of the beach traversed by the swash. The depressions will 
be broad, because they are thus better adapted to the move- 
ments of large volumes of water; and shallow, because the 
elevations between the depressions are also buried under the 
advancing and retreating waters and are kept worn down to a 
moderate height. Only near the upper zone of wave action, 
where the water invades the depressions but does not rise high 
enough to override the intervening elevations, are the depres- 



BEACH CUSPS 483 

sions continually scoured deeper and the unworn elevations left 
as pronounced ridges. Out toward the seaward margin of the 
submarine terrace, deposition rather than erosion prevails, and 
the delta scallops may rise higher than the seaward extension 
of the elevations which exist farther up the beach. 

There is a limit to the width to which the depressions, or 
shallow " channels," if we may so call them, can develop. In- 
asmuch as the enlargement of some necessitates the obliteration 
of others, enlargement will continue only so long as the impulse 
toward growth imposed on the more favored channels is suffi- 
ciently great to overcome the tendency of their neighbors to 
enlarge. Equilibrium will be established when adjacent chan- 
nels are of approximately the same size, and at the same time 
of a size appropriate to the volumes of water traversing them. 
If the waves are low and the volumes of water consequently 
inconsiderable, equilibrium will be reached while the channels are 
yet small. But if the waves are high and the volumes of water 
large, a perfect adjustment will not be reached until the chan- 
nels have attained great size. 

The remainder of the process is easily understood. With 
the water advancing repeatedly up a beach which is faintly but 
systematically channeled, as above indicated, there will be a 
constant tendency to push gravel and other debris farther up 
the slope in the depressed areas than in the intervening areas. 
Near the upper limit of wave action the depressed areas alone 
are invaded by water and are scoured deeper as the gravels are 
pushed back and the finer material dragged down to form the 
delta scallops. The intervening areas are fashioned into beach 
cusps, whose sharpened points divide the waters of the advanc- 
ing waves and concentrate the attack toward the heads of the 
depressions. The coarse material is constantly pushed into the 
cusp areas, the channels swept relatively clean. With a rising 
tide both channels and cusps are pushed progressively up the 
beach; with a falling tide some of the gravels may be dragged 
downward to give much elongated cusps. 

There ar^ a number of considerations which appear to sup- 
port the foregoing theory of beach cusp formation. The theory 
accounts for the degree of regularity observed in the spacing of 
beach cusps, since the spacing is dependent on the development 
of channels which do not reach equilibrium until of approxi- 



484 



MINOR SHORE FORMS 



mately uniform size. At the same time the considerable degree 
of irregularity in spacing occasionally observed is not incom- 
patible with the theory, since the degree of regularity in spacing 
depends on the progress which has been made toward the estab- 
lishment of perfect equilibrium. The occurrence of imperfect 
and compound cusps is readily explained as the product of wave 
action in channels not yet eroded to the standard size, as when 
two unusually small channels have not yet been fashioned into 
a single large one, and consequently give a compound cusp (Fig. 
145) near their upper limits. We should expect, on the basis of 
this interpretation, that irregular and compound cusps should be 
most characteristic of the early stages of development, and the 




"Si 

i-v-N.'.^v ••>♦• - »*••* '•'-•s •*?■•• *4fei« 



Fig. 145. — Beach cusps (after Jefferson) showing compound cusps at right. 



experiments with artificial cusps prove most conclusively that 
this is the case. One of the commonest occurrences in the 
experiments is the gradual moulding of irregular and compound 
cusps into simple cusps regularly spaced. 

The respacing of cusps with a change in size of waves may be 
thus explained: A given set is formed and driven up the beach, 
and then left by the falling tide. The size of waves changes, 
and new channels appropriate to them are formed. New cusps 
result, and as the tide rises these are in turn pushed up the beach. 
If the new cusps do not coincide in position with the older ones, 
when the latter are reached their ends will be eroded by the 
waters converging on them from between the new ones. Repe- 
titions of this process, with waves of decreasing size, will give 
several sets of partially preserved cusps, each set more closely 
spaced than the set above it. On the other hand, if a big 
storm drives in unusually high waves, big channels will be formed, 



BEACH CUSPS 485 

older sets of cusps will be quickly swept out of existence, and 
a single set of large, widely spaced cusps will be de- 
veloped. 

In the laboratory experiments difficulty was often experienced 
in getting the cusps started. The artificial beach was very 
smooth, of fairly uniform sand grains. It appeared that the 
difficulty was due to the regularity of the beach, on account of 
which the initiation of channels was delayed. In order to 
facilitate the process a series of closely spaced creases down 
the beach was made, after which the cusps began to form more 
rapidly. As already shown, the artificial creases did not control 
the number or position of the cusps and their intervening spaces, 
but the importance of initial depressions in the cusp-making 
process seemed clearly indicated. 

On Westquage Beach, Rhode Island, the writer has watched 
a series of parallel " creases," or rill lines, without any associ- 
ated cusps, develop into channels or intercusp spaces with 
fairly good associated sand cusps. Such observations are rela- 
tively rare, however, probably because the initial irregularities 
are often indistinct undulations in the beach surface or are 
soon transformed into such undulations; and because the succes- 
sive changes in the form of broad, shallow channels on a gravel 
or sand and gravel beach are difficult to trace. The " ribbed " 
structure occasionally reported by observers looking for cusps 
probably represents an early stage of cusp formation. 

The tendency of intersecting or criss-cross' waves would be 
continually to shift the sands first in one direction and then in 
another obliquely over the beach, and thus to prevent the forma- 
tion of systematic channels. This would account for the ob- 
served failure of such waves to form beach cusps, although they 
might attack cusps previously formed, or leave a beach with 
irregularities which might affect the formation of later cusps. 

In a similar way, to a less extent, a single series of oblique 
waves would not seem favorable to cusp formation, because of 
the lateral element in the movement of the water, which would 
continually tend to wash the interchannel elevations into the 
channels, and so to fill them up. 

It is not necessary to review all the details of beach cusp char- 
acteristics in connection with the theory set forth above. It is 
sufficient to state that the author has found no feature of 



486 MINOR SHORE FORMS 

beach cusps which is incompatible with the theory, while the 
assumed conditions of wave action appear to rest on a reason- 
able basis. 

LOW AND BALL 

The shoref ace zone, or possibly the inner margin of the offshore 
zone, is frequently characterized by submarine bars or ridges, 
separated by distinct longitudinal depressions and lying par- 
allel to the shoreline. English writers apply the name ball to 
the ridges and low to the depressions. The continuity of the 
ball is sometimes truly remarkable, Russell 30 describing exam- 
ples on the shores of Lake Michigan which " can be traced 
continuously for hundreds of miles." In this case " there are 
usually two, but occasionally three, distinct sand ridges; the 
first being about 200 feet from the land, the second 75 or 100 
feet beyond the first, and the third, when present, about as far 
from the second as the second is from the first. Soundings on 
these ridges show that the first has about 8 feet of water over it, 
and the second usually about 12; between, the depth is from 
10 to 14 feet .... They follow all the main curves of the 
shore, without changing their character or having their con- 
tinuity broken." Russell suggests that these balls may repre- 
sent accumulations of shore debris along the lines where the 
undertow loses its force during storms of varying degrees of 
intensity; but qualifies the suggestion with the statement that 
" the complete history of these structures has not been deter- 
mined." 

The balls of Lake Michigan were earlier described by Desor 31 , 
who in 1851 attributed them to transportation and deposition 
by " currents," and stated his belief that the elevated beaches 
about the Great Lakes were really submarine bars of the same 
type which had been exposed to view by a rising of the land. 
Whittlesey 32 treats them briefly as a product of " lateral cur- 
rents." In 1870 Andrews 33 called attention to the " subaqueous 
ridge or bar " which is " uniform in all the sand shores " at 
the head of Lake Michigan. Gilbert at first 34 considered the 
balls of the Great Lakes region as barrier beaches or spits 
built at the lake surface and later submerged by a rise of the 
waters; but later 35 decided that they were originally formed as 
subaqueous bars. Concerning the method of their formation 



LOW AND BALL 487 

he writes: " Under conditions not yet apparent, and in a man- 
ner equally obscure, there is a rhythmic action along a certain 
zone of the bottom. That zone lies lower than the trough 
between the greatest storm waves, but the water upon it is 
violently oscillated by the passing waves. The same water is 
translated lakeward by the undertow, and the surface water 
above it is translated landward by the wind, while both move 
with the shore current parallel to the beach. The rhythm may 
be assumed to arise from the interaction of the oscillation, the 
landward current, and the undertow." 

The earliest description of low and ball of which I find record 
is given by Hagen in his " Handbuch der Wasserbaukunst 36 ." 
Hagen considers the phenomenon a normal characteristic of a 
gently sloping sea-bottom, and refers to a popular belief that 
three parallel balls (" RifTe ") are always found in association. 
He shows, however, that the number is not constant, as many 
as five sometimes being revealed by careful soundings. The 
ridge nearest the shore is highest, those farther out progres- 
sively decreasing in altitude until the outermost may rise an 
almost imperceptible distance above the sea floor. In Hagen's 
opinion the ridges form where on-coming waves meet the under- 
tow, especially where the undertow is reinforced by backward 
moving water of normal oscillatory waves. 

A brief account of the form of parallel balls is given in Braun's 
" Entwickelungsgeschichtliche Studien an europaischen Flach- 
landskusten und ihren Dunen," under the caption " Das San- 
driff 37 ." He follows Lehmann 38 in considering the ball as a 
forerunner of the offshore bar or beach ridge, the ball being 
driven landward and ultimately raised above sealevel by the 
action of the waves. Observations of European examples lead 
to the conclusion that normally the landward side of the ball is 
steeper than the seaward slope. Otto, on the contrary, in a 
full description of these submerged ridges published in his work 
on " Der Darss und Zingst 39 " finds them more variable in form 
and in behavior. They are sometimes evenly, sometimes irregu- 
larly spaced, and often migrate seaward as well as landward. 
Sudden and marked changes in the ridges occur only with 
great storms. A comparison of wave lengths and the distances 
between ridges shows that no correspondence exists between 
the two measurements. Both Braun and Otto give a short 



488 MINOR SHORE FORMS 

bibliography of the subject, which should be consulted by those 
desirous of securing further data regarding the lows and balls of 
the Baltic shores and other coasts of continental Europe. 

Under the title " Low and Ball of a Sandy Shore 40 ," Cornish 
states that the building up of a " full " of sand in front of the 
breaker is accompanied by the excavation of a trough, at the 
back of the breaker. Beyond the trough there rises a sandbank 
which is called the ball, while the trough itself is the low. Ebb 
tide may reveal the surface of the ball, under which condition a 
lagoon occupies the low between the ball and the beach. 
Wheeler 41 also speaks of the low as a gully running parallel to 
the coast cut by the action of breakers, and is of the opinion 
that the ball may rise permanently above the water surface, 
causing a permanent lagoon or shallow creek in the adjacent low. 

Kemp 42 has recorded some valuable observations regarding 
the lows and balls of the Florida east coast. At Melbourne 
Beach, and for an indefinite distance north and south, the shore 
is normally bordered by a distinct channel varying in breadth 
from 15 to 60 yards and usually' not so deep but that bathers 
could walk across it to the bar beyond at low tide. The crest of 
the bar rose within a few inches of the water surface, but was 
never seen exposed. Those engaged in surf -fishing for " channel 
bass" become familiar with all changes in the low, for this is the 
channel in which the bass run. After maintaining a fairly con- 
stant position for three months in the winter of 1915-16, the bar 
migrated shoreward under the influence of heavy surf from a 
strong easterly gale. After the storm died down the bar con- 
tinued its shoreward progress until the low was reduced to a 
breadth of 5 yards, then 2 yards, and finally was extinguished. 
The next fall the fishermen found a new bar with broad channel 
intervening between it and the shore, just as at the beginning of 
the previous winter. 

In classifying the forms observed on the Great Lakes by 
Desor, Gilbert, Russell, and others, with those observed on 
tidal shores by Cornish and Wheeler, and giving the English 
names low and ball to the entire series, I have proceeded on the 
assumption that the two forms are similar in character and 
identical in origin, such differences as are noted being due to 
the changing water level in the case of the marine type. I must 
state, however, that this procedure is not based on any careful 



RIPPLE MARKS 489 

comparison of these forms as developed in lakes and in the 
ocean, and my classification is accordingly to be accepted with 
due reservation. While I have examined fairly good lows and 
balls along the sandy beach at Cape Henry, Virginia, and else- 
where on the Atlantic shoreline, I have not seen those of the 
Great Lakes ; nor have I made^ sufficient study of the examples 
observed to add anything of value to the discussion of their 
origin. 

RIPPLE MARKS 

The accumulation of sand and finer debris in parallel ridges 
and troughs somewhat resembling water waves in form, though 
not at all in origin or method of formation, was long ago recog- 
nized as a normal product of wave and current action. Under 
various names, such as " current mark," " wave mark," " ripple 
drift," " current drift," and " friction markings," the phenome- 
non now generally known as ripple mark has repeatedly been 
described. Although not infrequently found on sandy beaches, 
ripple marks are perhaps better developed on tidal flats and over 
the broad shallow bottoms of estuaries. They are not unknown 
on the deeper sea floor of the offshore zone, where their occur- 
rence to a depth of over 600 feet has been demonstrated. Ripple 
marks exposed by the falling tide may be delicately dissected 
by rill marks, an interesting example of this phenomenon having 
been described by Dodge 43 . 

Among the earlier accounts of ripple marks one of the most in- 
teresting is based on the little known work of an ingenious French 
engineer named Siau 44 . In 1841 this investigator published a 
brief note entitled " De Taction des vagues a de grandes pro- 
fondeurs," based on observations of ripple marks in deep water 
made with the aid of an ordinary sounding apparatus. While 
examining ripple marks, visible during quiet water, on the bed 
of a channel off the west coast of the Isle of Bourbon, Siau 
noted that the heavier particles of the sand tended to accumu- 
late in the troughs between the ridges, while lighter material 
was concentrated along the ridge crests. Profiting by this dis- 
covery, he coated a sounding lead with tallow, and lowered it to 
the sea floor where the depth was too great for direct visual 
observation. When brought to the surface the tallow some- 
times retained, adhering to it, only heavy particles of sand, in 



490 



MINOR SHORE FORMS 



Plate LIX. 




Photo by G. K. Gilbert, U. S. G. S. 

Sandstone slab showing fossil oscillation ripples. A later, smaller series of 
oscillation ripples had begun to form in the troughs of the main series. 



RIPPLE MARKS 



491 



which the surface of the tallow had convex form, showing that 
it had been pressed down into the trough between two ripples. 
In other cases the tallow was coated with lighter particles only 
and had a concave form, as a result of having been pressed 
down upon a ripple crest. At great depths, where the ripples 
were more closely spaced, two parallel bands of materials, differ- 
ing in specific gravity, would be impressed upon the tallow at 
the same time, the heavier material coating a convex ridge and 
the lighter a concave depression in the tallow. By this ingenious 
device Siau was able to prove the existence of ripple marks at a 
depth of 617 feet. 

The ripples described by Siau were believed by him to be 
due to the back-and-forth currents, which, as we have already 
seen, are produced on a sea-bottom by oscillatory waves. Such 
ripple marks are called " oscillation ripples," and are char- 
acterized by symmetry of crests, neither slope being steeper 




Fig. 146. — Oscillation ripples. 

than the other, since the ridges are built up by currents which 
operate from either side with approximately equal force. The 
crests are sharp and narrow as compared with the more broadly 
rounded intervening trough (Fig. 146). De la Beche 45 in his 
Geological Observer describes another type of ripple mark pro- 
duced by the action of a current flowing steadily in one direc- 
tion over a bed of sand. These "current ripples" have a 
long, gentle slope toward the direction from which the current 
comes, and a shorter, steeper slope on the lee side. Sand grains 
removed from the gentle slope are carried to the crest and 
dropped down the steeper slope, causing the ripples to migrate 
slowly with the current, much as sand dunes migrate with the 
wind. The asymmetry of profile of the current ripple is shown 
by Figure 147, and is apparent in Plates LX and LXI Barrell 46 and 
others restrict the term " ripple mark " to oscillation ripples, 



492 



MINOR SHORE FORMS 



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RIPPLE MARKS 493 

and employ the term " current mark " for the asymmetrical 
type. This usage has much to commend it, but is open to sev- 
eral objections. The fact that " current mark " is produced by 
water currents might lead to the inference that " ripple mark " 
is produced by water ripples, which is not at all the case. 
Ordinary waves rather than true ripples commonly produce 



Fig. 147. — Current ripples. 

oscillation ripple marks. There are, moreover, other markings 
produced by currents, as will appear on a later page. The term 
" ripple mark " is so firmly established in the literature to in- 
clude both the symmetrical and asymmetrical types that it seems 
wisest to follow this usage, prefixing the words " oscillation " 
and " current " to make clear the necessary distinction. 

Sorby 47 gave a very good description of current ripples in 
The Geologist for 1859, but failed to recognize the existence of 
wave-formed oscillation ripples, although he noted, and even 
pressed too closely, the analogy between true waves and ripple 
mark. For many years current-formed ripples were the only 
type recognized in most textbooks. Gilbert 48 in 1875 described 
briefly what appear to have been oscillation ripples, but explained 
them as the product of running water thrown into vibration by 
friction on the bottom, a theory apparently similar to the " in- 
termittent friction " theory of de Candolle, described below. 
In 1882, in opposition to the general view, Hunt 49 claimed that 
as a rule ripple marks are the product of oscillatory wave action, 
and supported his claim with observations based on the arti- 
ficial production of ripple marks, as well as with numerous 
citations of naturally formed ripples. He was evidently un- 
aware of the fact that Siau had supported the same theory some 
40 years earlier, and in a later paper 50 erroneously credited 
Forel with priority in the recognition of oscillation ripples. 



494 MINOR SHORE FORMS 

Hunt incidentally describes oscillation ripples in his paper " On 
the Action of Waves on Sea-Beaches and Sea-Bottoms 51 "; he 
also discusses the nomenclature of ripple marks at much length 
in a paper published in 1904 52 , and elsewhere quotes Lieu- 
tenant Damant, R.N., as having observed ripple marks while 
diving at depths of 60 and 70 feet 53 . 

In 1883, the year following the publication of Hunt's earliest 
paper quoted above, there appeared three important essays on 
ripple marks: one by de Candolle on " Rides Formees a la 
Surface du Sable Depose au Fond de l'Eau et autres Phenomenes 
Analogues/'; another by Forel on " Les Rides de Fond Etudiees 
dans le Lac Leman "; and a third by Darwin " On the Forma- 
tion of Ripple Mark in Sand." De Candolle 54 produced ripple 
marks artificially by experimenting not only with sand and vari- 
ous substances in powdered form covered by water, but also 
with liquids of varying viscosity covered with water and other 
liquids. Regarding sand or powder when mixed with water as 
a viscous substance, he concluded from his experiments that 
" When viscous material in contact with a fluid less viscous than 
itself is subjected to oscillatory or intermittent friction, result- 
ing either from a movement of the covering fluid or from a 
movement of the viscous mass itself with respect to the covering 
fluid, (1) the surface of the viscous substance is ridged perpen- 
dicularly to the direction of friction, and (2) the interval between 
the ridges is directly proportional to the amplitude of the friction- 
producing movement." That ripple marks depend on simple 
friction alone, and not on any change of level in the covering 
liquid such as occurs during wave action, de Candolle proved 
by an experiment with a rotating disc submerged in a tank of 
water. After submerging the disc and mixing an insoluble 
powder in the water, the apparatus was left until the powder 
settled on the disc and floor of the tank as an even film, and the 
water came to rest. An oscillatory rotary movement then ap- 
plied to the disc caused radiating ripples to form upon it, while 
no ripples formed on the stationary bottom, and the surface of 
the water remained quiescent. The author concludes that the 
formation of ripples in sand, whether under currents of air or 
under water currents, is identical in origin with the formation 
of water ripples under moving air. If the current moves always 
in one direction we have intermittent friction due to varying 



RIPPLE MARKS 



495 




496 MINOR SHORE FORMS 

velocities. Otherwise we have oscillatory friction due to alter- 
nating change of direction. Current ripples result from the 
first type of friction, oscillation ripples from the second. 

Forel 55 in his excellent essay on " Les Rides de Fond Etu- 
diees dans le Lac Leman " sets forth the mature results of studies 
which had been briefly mentioned by him in three communica- 
tions 56 of earlier date. Abandoning his first theory, that the 
formation of ripple marks was dependent in part upon the 
vertical pressure of water waves upon the bottom 57 Forel reached 
the following important conclusions as the result of many care- 
ful observations and experiments: (1) Current ripples are asym- 
metrical and migrate with the current like ordinary sand dunes, 
whereas oscillation ripples are stationary and symmetrical. (2) 
Each oscillation ripple is really a composite of two current 
ripples resulting from the action of two currents moving alter- 
nately in opposite directions, each current attempting to form 
the ridge into a current ripple migrating with it, but being de- 
feated when the return current tries with equal force to shape the 
ridge into a current ripple directed in the opposite sense. (3) 
The length of the water body has no direct effect on the spacing 
of the ripples. (4) Other things equal, the ripples are more 
closely spaced with increasing depth. (5) At a given depth, 
and with other conditions uniform, the ripples are more widely 
spaced with increase in coarseness of sand grains. (6) Ripples 
once formed do not experience a change in spacing as a result 
of diminishing amplitude of oscillation of the water, although the 
original spacing does depend upon the amplitude of oscillation, 
as pointed out by de Candolle. (7) For any given coarseness 
of sand grains there is a certain mean velocity of the oscillating 
currents which will produce ripples: lower velocities will fail to 
move the sand grains, and hence cannot build ripples, while 
higher velocities agitate the whole mass of sand so violently 
that no ripples can form. (8) The formation of ripples is ini- 
tiated by some obstacle or inequality on the surface of the sand, 
behind which sand grains accumulate in the eddy caused by its 
presence: this leaves a furrow on either side of the initial ridge, 
due tp the abstraction of sand accumulated in the ridge; and 
these furrows in their turn cause additional ridges to develop on 
their outer margins, and so on. (9) In a given locality, ripple 
marks almost always form with the same spacing, regardless of 



RIPPLE MARKS 



497 



the varying intensity of winds and waves affecting the water 
body; this is in consequence of laws 7 and 6 stated above. 
(10) The depth at which ripple marks may form is limited by 
the depth to which wave action may extend with sufficient 
energy to move the bottom sands; hence it depends on the size 
of the waves, and therefore in part indirectly on the size of the 
water body : in the Rhone the limiting depth is a few decimeters ; 
in Lake Geneva some ten meters; and in the ocean from 20 to 
188 meters, according to Lyell and Siau. Forel revised de Can- 
dolle's law regarding the relation of ripple spacing to amplitude 
of the friction-producing movement to read: " The breadth of 
the ripples, or the distance from one crest to another, is the 
length of the path followed during a single oscillation by a grain 
of sand freely transported by the water." The length of this 
pg^th varies directly as the horizontal amplitude of the oscilla- 
tory movement of the water, directly as the velocity of that 
movement, inversely as the density of the sand, and inversely 
as the size of the sand grains. 

Darwin's paper 58 " On the Formation of Ripple Mark in 
Sand " is especially noteworthy for its careful analysis of the 




Fig. 148. — Vortices involved in the formation of current ripple mark. 

vortices which are so important a factor in the construction of 
the ripples. When symmetrical oscillation ripples were sub- 
jected to the action of a steady current, Darwin noticed that 
not only did sand grains migrate up the weather slope of each 
ripple with the current, but that they also ascended the- lee 
slopes, apparently against the current. This proved conclu- 
sively the existence of such vortices as are represented in Figure 
148. Darwin then proceeded to study the vortices by watching 
the movements of a drop of ink released from the end of a fine 
glass tube at that point in the water where the action was to be 
observed. In this manner the vortices associated with the alter- 
nating currents which produce oscillation ripples were analyzed 



498 MINOR SHORE FORMS 

with a high degree of precision, and much light was thrown upon 
the method of ripple growth. Darwin concluded that " the 
formation of irregular ripple marks or dunes (current ripples) by 
a current is due to the vortex which exists on the lee side of any 
superficial inequality of the bottom; the direct current carries 
the sand up the weather slope and the vortex up the lee slope. 
Thus, any existing inequalities are increased and the surface of 
sand becomes mottled over with irregular dunes." The in- 
termittent friction to which de Candolle appealed is not essen- 
tial in this explanation of current ripples. Oscillation ripples 
of regular pattern are changed by a continuous current into 
regularly spaced current ripples; but a uniform current cannot 
of itself initiate regularly spaced ripple mark. " Regular ripple 
mark (oscillation ripples) is formed by water which oscillates 
relatively to the bottom. A pair of vortices, or in some cases 
four vortices, are established in the water; each set of vortices 
corresponds to a single ripple crest." Forel's conception of an 
oscillation ripple as a composite of two dunes (current ripples) 
formed alternately by oscillating currents is regarded as correct; 
but his law for the relation of ripple spacing to amplitude of 
oscillation is believed to require some modification. 
- Further studies of ripple-forming vortices were made by Mrs. 
Hertha Ayrton 59 the results of which were not published until 
1910. With the aid of well-soaked grains of ground black 
pepper, or of particles of potassium permanganate dissolving 
and coloring the water while the latter was in oscillation, she 
observed the formation of vortices and endeavored to explain 
the mechanics of their growth. Although she expressed dis- 
agreement with the conclusions of Darwin and others on certain 
points, most of her results afford essential confirmation of their 
main contentions. Some doubt must attach to certain of her 
deductions, such as one to the effect that no ripple-forming 
vortex occurs in the lee of an obstacle over which a steady cur- 
rent is passing and hence " a steady current is unable either to 
generate or to maintain ripple-mark." 

The British Association Reports for the years 1889, 1890, and 
1891, contain three papers by Reynolds 60 on the action of 
waves and currents in model estuaries, in which are some valu- 
able observations regarding what may well be termed giant 
tidal ripples. While experimenting with artificial tidal currents 



RIPPLE MARKS 




Photo by G. K. Gilbert. 

Giant current ripples near Annisquam, Massachusetts, showing irregular 
pattern due to interference of wave and tidal currents. 



500 MINOR SHORE FORMS 

Reynolds discovered that current ripples were formed in the 
model estuaries. By making due allowance for the difference 
in size between the model estuaries and those in nature, he 
concluded that real tidal currents ought to produce very large 
current ripples, possibly 7 or 8 feet in height and 80 to 100 feet 
apart 61 . Some years later Vaughan Cornish 62 discovered nat- 
ural tidal ripples or " sand waves " of the same type as those 
produced artificially by Reynolds, having a height of 2 feet and 
an average distance of more than 37 feet from crest to crest. 
In two later papers 63 Cornish describes giant tidal ripples more 
fully, and illustrates their essential features with a large series 
of beautiful photographs. Some of these ripples have a height 
of nearly 3 feet above the intervening troughs, and a distance 
between crests of from 66 to 88 feet in extreme cases. The 
giant ripples are often covered with ordinary ripple mark, and 
while Cornish recognized that the larger forms were produced 
by the continuous steady flow of tidal currents, he was at first 
inclined to invoke pulsatory currents in order to explain the 
smaller ripple mark 64 . This theory seems to be a survival of 
de Candolle's erroneous idea that " intermittent friction " was 
essential to the production of current ripples, and is practically 
abandoned by Cornish in his more recently published book on 
" Waves of Sand and Snow 65 ." Gilmore 66 describes tidal ripples 
on the Goodwin Sands having a height of " two or three feet," 
and Kindle 67 reports " mammoth tidal ripples " in estuaries of 
the Bay of Fundy varying in length from 2 feet up to 15 or 20 
feet, and in height from 6 inches to nearly 2 feet. Gilbert 68 
measured examples near Annisquam, Massachusetts, which were 
15 feet in length, and 15 inches high, Plate LXII. River currents 
as well as tidal currents are capable of forming giant ripples, and 
Kindle 69 describes examples formed on a broad sandbar in the 
Ottawa River at time of flood which measured 30 to 45 feet in 
length and from 1 to 2 feet in height. The same author quotes 
Pierce as authority for the existence in the San Juan "River in 
Utah of examples rising 3 feet above the adjacent troughs. Un- 
fortunately Pierce 70 improperly applies the term " sand wave " to 
the water wave formed at the surface of a current passing over 
true sand waves or giant ripples. It is not clear that Pierce 
either saw or measured the giant sand ripples, supposed by him to 
have caused the surface water waves to which his figures apply. 



RIPPLE MARKS 501 

It should be noted that all of the giant ripples referred to 
above belong to the unsymmetrical type; they are true current 
ripples. So far as I am aware no giant oscillation ripples have 
ever been observed along modern shores. It may be doubted 
whether tidal currents could form symmetrical ripples, notwith- 
standing Reynold's suggestion to the contrary 71 . The flow and 
ebb of the tide constitutes an oscillating current, it is true; but 
the currents are often of unequal force. Where equally strong, 
each current persists long enough to remodel the ridges formed 
by the preceding current, giving them an asymmetrical form 
appropriate to the current operating last. On the other hand, 
Gilbert 72 has described structures in the Medina sandstone 
formation of New York which he believes to be giant ripples 
of the symmetrical type formed by oscillating currents due to 
wave action. In dimensions these ridges were similar to the 
average examples of tidal ripples described by Cornish, having 
a height of from 6 inches to 3 feet and a distance from crest to 
crest of 10 to 30 feet; but their nearly symmetrical form did 
not suggest a similar origin. Gilbert reached the tentative con- 
clusion that they were formed by waves 60 feet high in deep 
water of a broad ocean. This conclusion was criticized by 
Fairchild 73 , who advanced convincing arguments in support of 
the opinion that the forms in question were beach structures, 
possibly successive beach ridges built on the strand. Branner 74 
suggested that they might represent fossil beach cusps seen in 
cross-section. 

Some interesting experiments on the relation of current ve- 
locity to ripple-mark formation were made by Owens 75 , who 
published his results in 1908. He found that currents from 0.85 
to 2.5 feet per second produced or maintained a rippled surface 
on sand; but that a velocity of 2.5 feet per second and above 
swept the surface free of ripples. 

In 1911 A. P. Brown 76 published a paper entitled " The 
Formation of Ripple-Marks, Tracks and Trails " in which he 
endeavored to show that asymmetrical ripples (current ripples) 
were formed by deposition, whereas symmetrical ripples (oscil- 
lation ripples) resulted from the erosion of a formerly smooth 
bottom consequent upon the rippling of overlying water by 
wind action. His conclusions do not appear to be supported 
by a sufficient body of convincing evidence, and are opposed 



502 MINOR SHORE FORMS 

by theoretical considerations and by the great body of experi- 
mental data already referred to on previous pages. Unfortu- 
nately, in presenting his theory Brown does not consider the 
important results obtained in the many previous investigations 
of ripple marks. 

A similar criticism must be urged against the work of Epry 77 
who in 1912 published a paper on " Les Ripple-Marks " in the 
Annales de lTnstitut Oceanographique. Epry states that no 
one before him has been able accurately to determine the causes 
of ripple marks and that no previous theory of their origin is 
satisfactory. He fails, however, to show wherein earlier the- 
ories are defective and from his essay it does not appear that he 
was acquainted with the various publications cited above. 
Current ripples and oscillation ripples are not distinguished by 
him, and a highly specialized theory of origin, impossible of 
application to the majority of ripple surfaces, is developed. It 
is not necessary to criticize Epry's theory in detail, but a gen- 
eral idea of its essential nature may be gathered from the fact 
that it involves the remarkable assumption that ripples are 
formed where an ebbing tidal current returning from the shore 
is cut transversely by another current deflected along a depres- 
sion in the sea floor, and that the ripples are aligned in the 
direction of (parallel to) the transverse current. No less re- 
markable is Epry's statement that ripple marks are the work of 
tides alone. 

We have already noted that current ripples, like sand dunes, 
normally migrate slowly in the direction of the current which is 
fashioning them. Vaughan Cornish 78 discovered, however, that 
in shallow water when the current attains a velocity of about 
2.2 feet per second, the ripples travel upstream or against 
the current. This observation was later confirmed by Owens 79 , 
and the phenomenon is described by Gilbert 80 in the following 
words: "When the conditions are such that the bed load is 
small, the bed is molded into hills, called dunes, which travel 
downstream. Their mode of advance is like that of eolian 
dunes, the current eroding their upstream faces and depositing 
the eroded material. on the downstream faces. With any pro- 
gressive change of conditions tending to increase the load, the 
dunes eventually disappear and the debris surface becomes 
smooth. The smooth phase is in turn succeeded by a second 



RIPPLE MARKS 



503 




■ 







504 MINOR SHORE FORMS 

rhythmic phase, in which a system of hills travels upstream. 
These are called anti-dunes, and their movement is accomplished 
by erosion on the downstream face and deposition on the up- 
stream face. Both rhythms of debris movement are initiated 
by rhythms of water movement." Pierce 81 states that the 
anti-dune movement is best seen " only on heavily loaded silt 
streams/ ' and cites cases of the phenomenon in the San Juan 
River in Utah. 

The best recent essay on ripple marks is a paper by Kindle 82 
entitled " Recent and Fossil Ripple Mark," published in 1917. 
This author presents an excellent summary of his own exten- 
sive observations, distinguishes the different types of ripple 
marks and their methods of origin, and gives many references 
to the work of others. The abundant illustrations contain 
some of the best views of ripple marks ever published. Kindle 
studied different types of ripples by means of plaster casts, some 
of which were secured at depths ranging up to 27 feet by means 
of a specially devised apparatus. Siau's experiments were also 
imitated by lowering to the bottom, at any depth, a rectangular 
plate of sheet iron or "zinc, the under surface of which had been 
coated with vaseline. Where ripple marks occurred, parallel 
lines of sand adhering to the vaseline indicated the position 
and spacing of the ripple crests. On the basis of his studies 
Kindle concludes that the length of asymmetrical or current 
ripples varies with the velocity of the current, with the volume 
of sediment in suspension, and possibly also with depth. " A 
strong current carrying a maximum load of sand probably forms 
ripple mark of large amplitude (length) where a slightly loaded 
current having the same velocity would leave no ripple mark." 
The author is less certain about the factors controlling symmet- 
rical or oscillation ripples, but thinks coarseness of sand, depth 
of water, and length of the water waves are of chief importance. 
In studying Kindle's valuable paper the reader must guard 
against misapprehension arising from his use of the term " am- 
plitude " to denote the length of both sand waves and water 
waves. 

Some of Kindle's conclusions must be regarded as open to 
question. This is particularly true of the following general- 
izations: " On the shores of lakes where ripple mark is due 
entirely to wave action it always runs parallel with the coast- 



RIPPLE MARKS 505 

line. Ripple mark along the sea coast is generally the work of 
tidal currents which follow the shoreline. These current-made 
ripple marks consequently trend at right angles to the coast- 
line. Lake shore and sea shore ripple mark are thus differently 
oriented with respect to their adjacent shorelines, the former 
trending with the shoreline, the latter at right angles to it 83 " ; 
"the abundance of the wave-made type of ripple mark in a 
sandstone formation and the absence of the asymmetrical type 
would indicate its formation under lacustrine conditions. The 
great predominance on the other hand of the asymmetrical 
type of ripple mark would as certainly suggest the work of 
tidal current action and marine conditions 84 ." My own ob- 
servations of ripple marks do not tend to support the conclu- 
sions expressed in these quotations. While it is true that wave 
refraction often brings about a more or less perfect parallelism 
between wave crests and the shoreline in the immediate vicinity 
of the latter, the parallelism is, on the other Uiand, often far 
from perfect; and a few feet from the shore the waves not in- 
frequently trend at large angles to the shore. I have, on a number 
of occasions, observed ripples on the bottoms of ponds and lakes 
which were, like the waves which formed them, not parallel to 
the shoreline even when but a few feet distant from it. The 
supposed restriction of oscillation ripples to lacustrine deposits 
seems equally doubtful. Some of the best oscillation ripples I 
have ever seen were formed on tidal flats, bordering the Long 
Island shore, by wave action when shallow water covered the 
flats at high tide. Other good examples may frequently be seen 
in shallow ponds and abandoned channels on river flood plains. 
Kindle' s discriminations between marine and lacustrine deposits 
(see pp. 48 to 51 of his essay), and between lacustrine and fluvia- 
tile deposits (pp. 52 and 53), on the basis of the type of the con- 
tained ripple • marks, must therefore be accepted with caution, 
just as truly as must his deductions regarding the direction of 
ancient shorelines based on the orientation of fossil ripple marks. 
Even where a geological formation contains ripple marks ex- 
hibiting a remarkable uniformity of orientation over wide areas, 
as in a case described by Hyde 85 in a valuable paper published 
a few years ago, and where the existence of some definite control 
of ripple direction is clearly demonstrated, there may still be 
room for a variety of interpretations as to the position of former 



506 



MINOR SHORE FORMS 



f i f ■ 




RIPPLE MARKS 507 

shorelines. An interesting attempt to deduce paleogeographic 
conditions from a discriminating study of large fossil current 
ripples will be found in a recent paper by Bucher 86 . 

The simultaneous action of continuing currents and oscilla- 
tory wave motion, as well as the action of intersecting cur- 
rents or intersecting systems of waves, give rise to a variety of 
peculiar ripple forms. Thus oscillation ripples may be made 
slightly asymmetrical by a feeble current, or faint oscillation 
ripples may be superposed on strongly developed current rip- 
ples. Strong oscillatory wave action or secondary current action 
may give to a series of current ripples the peculiar pattern shown 
in Plate LXIV, if the waves or current advance obliquely over 
the earlier formed current ripples. " Interference ripple mark" 
(Plate LXV) results when two sets of symmetrical ripples are 
formed by two systems of waves crossing nearly at right angles. 
The cell-like pattern of some interference ripple marks led Hitch- 
cock to regard them as " tadpole nests." Examples of these and 
other abnormal ripple types are described and figured by Kindle. 

Ripple marks have repeatedly been discussed in connection 
with the interpretation of fossil ripples found in sedimentary 
rocks. We need mention but a few of these discussions in the 
present connection. As early as 1831 Scrope 87 described fossil 
ripple marks found on slabs of marble, and explained them as 
.due to the oscillatory movements of shallow water. Darwin 88 , 
starting from the very questionable assumption that a great 
ebb and flow of the tide is essential to the formation of numerous 
ripples, concluded that the presence of a large number of ripple 
marks in a geological formation indicated with a considerable 
degree of probability that the tides of early times rose higher 
than those of today. Van Hise 89 figures and describes one type 
of oscillation ripples, and emphasizes their value as criteria 
for determining the original attitude of steeply inclined strata. 
Gilbert 90 suggested the possibility of an analogy between ripple 
marks and vibrations in elastic bodies, basing the suggestion 
on observations of fossil ripple marks in the Jurassic limestone 
and Triassic sandstones of Utah. 

Spurr 91 shows that where continuous deposition takes place 
from a current which constantly maintains asymmetrical ripples 
on the surface over which it flows, the forward movement of 
the ripples combines with the deposition of heavier and larger 



508 



MINOR SHORE FORMS 




RIPPLE MARKS 509 

fragments in the troughs and lighter particles on the crests, to 
give a peculiar type of false bedding in the resulting formation. 
Jagger 92 criticized Spurr's conclusions on the ground that his 
own experiments and observations indicated that ripple marks 
could not be produced in heterogeneous material; but Spun* 93 
met the criticisms with a fuller discussion of the matter in which 
his original contention is well sustained A short time pre- 
viously Sorby 94 had described a somewhat similar phenomenon 
in a paper printed almost exactly half a century after the pub- 
lication of his first account of ripple marks, already cited. From 
an examination of the " ripple drift " type of false bedding in 
rocks Sorby believed one could " ascertain with approximate 
accuracy, not only the direction of the current and its velocity 
in feet per second, but also the rate of deposition in fractions of 
an inch per minute 95 ." 

The finding of ripple-marked limestone has been the occasion 
of two lines of reasoning regarding the origin of the rock, both 
based on the assumption that ripple marks cannot be formed in 
deep water. According to one argument, the ridges and troughs 
are not true ripple marks, since limestones are necessarily formed 
in deep water; the other argument holds such limestones to 
be necessarily of shallow water origin, because the ridges and 
troughs are true ripple marks. An example of the former argu- 
ment may be found in Locke's early report 96 on " waved strata " 
of Ordovician limestone in southwestern Ohio; while Foerste 97 
presents the second point of view in discussing the origin of 
Ordovician and Silurian beds in this same general region. The 
frequent occurrence of unusually large ripple marks in lime- 
stone has been noted by Gilbert 98 , Moore and Hole 99 , Cushing 100 , 
Miller 101 , Kindle and Taylor 102 , Udden 103 , Prosser 104 , and others, the 
distance from crest to crest of these ripples varying from one 
foot to two or three feet in most cases, but reaching a maximum 
of nearly six feet in an example described by Udden. Wooster 105 , 
Kindle 106 , and Udden 107 record the association of ripple marks in 
limestone with the remains of deep water organisms; while 
Kindle 108 regards the large size of the ripples as independent 
evidence of a considerable water depth. Shannon 109 found large 
ripple marks in limestone associated with sun-cracks, but does 
not state whether the ripples were of the symmetrical or asym- 
metrical (current) type. The present writer published in the 



510 MINOR SHORE FORMS 

Journal of Geology for November, 1916, a review of the litera- 
ture on ripple marks under the title " Contributions to the 
Study of Ripplemarks 110 ," based on studies made for the present 
work. 

The writer's observations of beaches incline him to the opinion 
that there is comparatively little chance for the preservation 
and incorporation in the geological record of ripple marks origi- 
nally formed on typical beaches. As we have already seen, the 
beach is a temporary and constantly changing deposit, and 
while both oscillation and current ripples form on sandy beaches, 
their subsequent destruction is almost certain, even though 
streams discharging sediment upon the beach may temporarily 
bury them. Ripple marks formed on the sea-bottom in the 
offshore zone stand a better chance for preservation, as also do 
those on tidal mud flats and sand flats. Under none of these 
circumstances, however, would the opportunities for preserva- 
tion seem so good as on river flood plains and deltas. Here 
ripple marks of both principal types are readily formed in 
shallow ponds, lakes, and stream channels, and later deposition 
from spreading flood waters may quietly bury them in places 
secure from future disturbance. Fossil ripple marks are there- 
fore not to be regarded as an evidence of beach deposits, unless 
associated with independent evidence of a much more reliable 
character. 

Even where fossil ripple marks have a marine origin, their 
position furnishes no satisfactory clue to the position of the 
former shoreline. Both on the beach and in the offshore zone 
the axes of the ripples may lie at any angle to the shoreline, as 
has been pointed out in earlier pages. Current ripples with 
axes at variable angles to the shore are very frequently found 
in low depressions along the beach. Water from the rising tide 
or from storm waves entering such depressions at any low point, 
flows through it developing transverse series of asymmetrical 
ridges. Oscillation ripples may take any position on the beach, 
and one occasionally sees there a checkerboard pattern of little 
hollows and mounds representing two sets of oscillation ripples 
crossing each other at right angles. In the offshore zone both 
types of ripples have been observed making high angles with 
the shoreline. 

Regarding the relation existing between size of ripple marks 



RIPPLE MARKS 



511 




512 MINOR SHORE FORMS 

and depth of water in which they were formed, theoretical con- 
siderations based on the nature of current and wave action 
would seem to compel the following conclusions: (1) Giant 
current ripples manifestly cannot be produced in extremely 
shallow water; but aside from this narrow limitation, both 
large and small current ripples may be formed in either shallow 
or deep water. (2) Large oscillation ripples cannot be formed 
in shallow water, for large oscillatory waves are impossible 
where the depth is small. (3) Both large and small oscillation 
ripples may be formed in deep water; whether the ripples will 
be large or small will depend upon a number of factors, among 
which the length and height of the wave and the depth of the 
water are most important. The fact that small ripples alone 
are most commonly found in sandstones, while both large and 
small ripples occur in limestones, is in accordance with con- 
clusions (2) and (3) above; while the predominance of large 
ripples in limestones might be expected to follow from the sixth 
law enunciated by Forel: " Ripples once formed do not experi- 
ence a change in spacing as a result of diminishing amplitude of 
oscillation of the water." Large ripples once formed in deep 
water tend to remain, and so to be preserved by burial, despite 
later oscillations which would of themselves have produced 
closely spaced ripples. 

RILL MARKS 

The water left in the sands of the upper part of the beach 
after the retreat of the tide or after the dying down of storm 
waves, often carves tiny drainage channels as it flows back to 
the sea. These miniature river systems are known as rill marks, 
and are not formed below sealevel. They may, however, be 
formed on any slope of fine-grained, unconsolidated material 
from the upper portion of which there is a seepage of water, 
and hence their presence in consolidated rocks is no proof that 
the rocks in question represent beach deposits. As is the case 
with ripple marks, the probability of preservation is not so great 
when rill marks are formed on beaches as when they are formed 
elsewhere. 

The pattern of rill marks (Plate XL VI) often resembles rather 
closely that of branching plant stems; indeed, so close is the 
resemblance that casts of rill marks found in sedimentary rocks 



RILL MARKS 



513 
Plate LXVII. 





Photo by E. M. Kindle. 

Plaster cast of swash marks left by four successive waves on the sandy shore 

of Lake Erie. 



514 MINOR SHORE FORMS 

have repeatedly been mistaken for ancient plant remains. In 
1873 Nathorst 111 published a paper in which he showed that rill 
marks and other markings on the strand had been regarded by 
many authors as phenomena of vegetable origin. I have not 
seen this paper, but the same idea is briefly presented in the same 
author's valuable memoir entitled " Om spar af nagra evertebre- 
rade djur m. m. och deras paleontologiska betydelse 112 ," which 
appeared eight years later. This memoir contains an excellent 
bibliography of papers treating mechanical markings and the 
tracks of animals on the shore as vegetable remains, and gave rise 
to a spirited controversy in which de Saporta 113 , Nathorst 114 , 
Gaudry 115 , Williamson 116 , and others took an active part. Wil- 
liamson made plaster casts of natural rill marks and showed their 
identity with many so-called fossil plants. The reader who 
would follow this phase of the subject further will find addi- 
tional references to the literature in the works of the authors 
just cited. 

Rill marks of an unusually delicate pattern have been briefly 
described by Dodge 117 who found them confined to the seaward 
side of previously formed ripple marks on Winthrop Beach, 
Massachusetts. Jagger 118 produced artificial rill marks, and de- 
scribed the process of their development. Grabau 119 classes 
with rill marks those branching distributaries of small streams 
which debouch upon a beach or other sandy or clayey plain. 
Rill marks of whatever type present no difficulties as to their 
origin, while in form they are so simple and unimportant as to 
require no special discussion. 



SWASH MARKS 

When a wave breaks at the foot of a gently inclined beach, 
part of the water glides up the slope in a thin sheet known as 
the " swash." After the retreat of the swash the greatest 
advance of its irregular margin is often indicated by a thin, 
wavy line of fine sand, mica scales, bits of seaweed and other 
debris, commonly referred to as a " wave mark" (Plate LXVII). 
Since there are a variety of marks left on sand by wave action, 
and the present feature is peculiarly a product of the swash, I 
have given it the name of " swash mark." Although too deli- 
cate a feature to attract much attention on the modern shore, 



BACKWASH MARKS 



515 




u 



516 



MINOR SHORE FORMS 



Plate LXIX. 



■Vd;jtfri< '•'-- > ' ; \ /» - u 




Photo by E. M. Kindle. 

Plaster cast of backwash marks (after Kindle). 



BACKWASH MARKS 517 

the swash mark is one of the best proofs of beach action usually 
preserved in sedimentary rocks. When found in the fossil con- 
dition swash marks may throw light on other buried shore 
forms with which they are associated 120 . 



BACKWASH MARKS 

The return flow of the swash down the beach often develops a 
peculiar criss-cross ridge pattern (Plate LXVIII) in the sand re- 
sembling " the overlapping scale-leaves of some Cycadean stem." 
Williamson 121 regarded similar ridge patterns as the product of 
intersecting ripple marks trenched by subsequent rills. The 
illustrations given by him do not suggest such an origin, and I 
am inclined to regard the phenomena observed by him as iden- 
tical in origin with the criss-cross pattern which I have observed 
in process of formation by the backwash. Kindle 122 figures an 
excellent example of the phenomenon under the title " imbricated 
wave sculpture" (Plate LXIX), and ascribes it to "the action of 
very small waves lapping and crossing each other from opposite 
sides of a miniature spit." It is a matter of common observa- 
tion that two projecting lobes of the swash are often directed 
toward each other as they rush up the beach slope, and that the 
return backwash from the two meet at an angle in their de- 
scent. The resultant crossing of currents would be similar to 
that described by Kindle, and might explain the frequent devel- 
opment of the imbricated pattern on beaches subjected to the 
action of breaking waves. On the other hand I have observed 
cases in which it seemed to me the phenomenon was caused by a 
single backwash current. The thin sheet of water returning 
down the beach slope appeared to be split into diverging minor 
currents by every patch of more compact sand or particle of 
coarser material which impeded its progress, and the crossing 
of these minor currents resulted in the criss-cross pattern in the 
sand. Whatever the precise mode of formation, the phenom- 
enon is normally the product of backwash from waves breaking 
on the beach slope, and may appropriately be called backwash 
mark. 



518 



MINOR SHORE FORMS 



SAND DOMES 

When the tide is advancing up the slope of a sandy beach, 
and the swash from a large wave first sweeps over a portion of 
the beach previously dry, the disappearance of the water may be 
accompanied by the appearance of miniature domes or blisters 
which arise at various points over the area newly subjected to 
the action of the swash. These domes usually vary from two to 
eight inches in diameter, and may rise an inch or possibly more 
above the level surface of the beach. If the curious observer will 
gently remove one side with a knife blade, he will discover that 
the dome is hollow as shown in Figure 149, the vertical height 
of the air chamber corresponding to the height of the dome 
surface above beach level. 

The formation of these sand domes may be explained as fol- 
lows: Before the swash reaches the area in question, the beach 




Fig. 149. — Sand dome. 



Arrows show movement of air as water sinks 
down from surface. 



sands are dry, and air fills the pore spaces between the sand 
grains. The first advance and retreat of the swash saturates 
the surface layer of the sand, water replacing air in the pore 
spaces to a depth of one-fourth or one-half inch. Penetration 
of the water to greater and greater depths can be accomplished 
only through expulsion of the air previously occupying the pore 
spaces. Part of the air escapes directly through the surface 
film of wet sand, and may be seen bubbling from countless 
tiny holes before the swash has returned down the beach. In 
other places the surface film of wet sand is quite air-tight, and is 
locally raised as a perfect miniature dome by air forced upward 
through the action of water descending in adjacent areas. Where 
the waves wash a layer of wet sand over an air-filled hole bored 



SAND DOMES 



519 




GO 



520 MINOR SHORE FORMS 

by some small mollusc the formation of the dome may be facili- 
tated. It is hardly necessary to remark that the sand domes, 
which have not to my knowledge been previously described, are 
very ephemeral features. 



SHORE DUNES 

The sand dunes, formed from beach sands along the shore, 
have received much attention in descriptions of shore forms. 
They are extensively developed along the coast of the Landes 
in southwestern France, where they attain heights of from 80 
to 90 meters in places, cover a belt from 2 to 6 miles in breadth, 
and have overwhelmed houses and churches causing whole towns 
to be abandoned by the inhabitants 123 ; along the coast of the 
Netherlands (Plates LXX and LXXI) and Denmark, where they 
are not so high as in France, but nevertheless serve as an im- 
portant barrier between the sea and the lowlands reclaimed from 
tidal waters, attaining a height of 30 meters on the Danish coaut; 
and on the south and east coasts of the Baltic, where they cover 
broad belts on the Darss foreland and near Swinemunde, and 
rise to an altitude of 60 meters on the narrow bay bars of the 
Frische Haff and Kurische Haft 124 . On the Atlantic coast of 
the United States shore dunes have an extensive development 
near Provincetown, Massachusetts, and on Cape Canaveral, 
Florida; while smaller areas on Sandy Hook and other parts 
of the New Jersey coast 125 , near Cape Henry, Virginia 126 , and on 
the offshore bars of the Carolina coast 127 are noted for their 
dunes. Inasmuch as these dunes are the product of wind 
action, and are only indirectly related to shore processes, it is 
not desirable to consider them at length in the present connec- 
tion. The only dunes which have special interest for the student 
of shore processes are those occurring in the form of parallel 
ridges on a beach plain. These " dune ridges " have already 
been fully discussed in Chapter IX. 

The student desiring to pursue further the study of dunes 
should consult the early work of Bremontier 128 bearing the title 
"Memoire sur les Dunes." 

Solger's "Dunenbuch 129 ," includes a treatment of shore dunes, 
and Sokolow, in his important work entitled " Die Dunen: 
Bildung, Entwickelung, und innerer Bau 130 ," discusses sand 



SHORE DUNES 



521 




o 

w 

pf 

o 

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0) 
a 

m 



522 



MINOR SHORE FORMS 




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a 
o 

-a 



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SHORE DUNES 523 

dunes of all types and gives copious references to the literature 
of the subject. He reaches the conclusion that over 90 per cent 
of the shore dunes of Europe occur on coasts which are sub- 
siding, or which at least are being undermined by wave attack; 
and interprets this to mean that the undermining action con- 
stantly uncovers fresh supplies of sand and hinders the growth 
of vegetation which might protect the sand from wind action, 
whereas on a rising coast sand deposits may be raised above 
the reach of the waves and be replaced by clay or other sand- 
free sediments 131 . 

If Sokolow's conclusion and interpretation were valid, the 
presence or absence of shore dunes would become a matter of 
much importance in determining past changes of level. Un- 
fortunately, the criteria accepted by this author as satisfactory 
proofs of land sinking would probably result in the classifica- 
tion of 90 per cent of all the coasts of the world as sinking coasts ; 
whereupon the occurrence of 90 per cent of the dunes upon 
such coasts would lose significance. Neither can we agree that 
retrograding coasts necessarily favor, and prograding coasts 
hinder, dune formation. The almost complete absence of 
shore dunes on some of the European and American coasts 
suffering most from wave attack, and the magnificant develop- 
ment of dunes on such prograding shores as those of the Darss, 
Swinemunde, and Cape Canaveral, point to a different inter- 
pretation. The development of shore dunes depends upon a 
number of variable factors, among which are the direction of 
the wind (offshore or onshore), the rapidity with which debris 
is supplied to the shore, the size of the debris particles, the 
nature of the climate, and the stage of development attained 
by the shoreline. It may be doubted whether very slow changes 
of level constitute a factor of importance. In any case, it 
would seem that a retrograding shoreline, along which more 
material is being taken from the land than is added to it, would 
present conditions unfavorable to the extensive accumulations 
of shore dunes; whereas, it is certain that the dunes of the 
Darss, Swinemunde, and Canaveral, and probable that those 
of the Landes, owe both their formation and their preservation 
to the prograding of sandy shores. 



524 



MINOR SHORE FORMS 





W 



u 



REFERENCES 525 

RESUME 

In the present chapter we have turned our attention to those 
minor forms of the shore zone which have no great significance 
in the general history of the shore cycle, but which nevertheless 
appeal to the interest of every observer who studies the meeting 
place of land and water with an inquisitive mind. It has been 
shown that the triangular cusps of sand or gravel built by waves 
upon the beach have given rise to much discussion and to several 
theories of origin. These theories we have examined and criti- 
cized in the light of new evidence as to the distribution and char- 
acters of the cusps. The low and ball of sandy shores have been 
briefly treated, and the puzzling problem of their origin indicated 
by citations from different observers. We have examined some 
of the rather abundant literature relating to the interesting phe- 
nomena of ripple marks, and have noted the value which these 
forms have to the geologist who must interpret the origin and 
structure of sedimentary rocks. Rill marks, swash marks, and 
the marks produced by the backwash in turn received brief 
attention; while the curious but very temporary sand domes 
have been described and their origin explained. Finally the 
interesting sand dunes occurring on the shore have been men- 
tioned, and suggestions offered as to where the student may find 
elaborate discussions of these forms, which do not properly lie 
within the province of a book devoted to shore processes and 
shoreline development. 

REFERENCES 

-1. Palmer, H. R. Observations on the Motions of Shingle Beaches. 

Phil. Trans, of the Royal Society. CXXIV, Pt. I, 573, 1834. 
2. Lane, Alfred C. The Geology of Nahant. Bost. Soc. Nat. Hist., 
Proc. XXIV, 91-95, 1888. 
- 3. Shaler, N. S. Sea and Land. 252 pp., New York, 1894. 

4. Shaler, N. S. Beaches and Tidal Marshes of the Atlantic Coast. 
National Geogr. Monogr. I, 164-165, 1895. 
♦ 5. Cornish, Vaughan. On Sea Beaches and Sand Banks. Geog. Jour. 
London. XI, 637-639, 1898. 

6. -Jefferson, M. S. W. Beach Cusps. Jour, of Geol. VII, 242, 1899. 

7. Branner, J. C. The Origin of Beach Cusps. Jour, of Geol. VIII, 

481-483, 1900. 

8. Branner, J. C. Editorial Note. Jour, of Geol. IX, 535, 1901. 

9. Jefferson, M. S. W. Shore Phenomena on Lake Huron. Jour, of 

Geol. XI, 123, 1903. 



526 MINOR SHORE FORMS 

10. Agassiz, Alexander. The Coral Reefs of the Tropical Pacific. Mem- 
oirs Museum Comparative Zoology. XXVIII, 322, 1903. 
'II. Wilson, A. W. G. Cuspate Forelands Along the Bay of Qumte. Jour, 
of Geol. XII, 106-132, 1904. 

12. Jefferson, M. S. W. On the Lake Shore. Normal College News. 

Ill, 1905. 

13. Johnson, Douglas W. Beach Cusps. Bull. Geol. Soc. Am. XXI, 

599-624, 1910. 

14. Kemp, James F. Unpublished field notes. 

15. Jefferson, M. S. W. Beach Cusps. Jour, of Geol. VII, 238, 1899. 

16. Jefferson, M. S. W. On the Lake Shore. Normal College News. 

Ill, 10, 1905. 

17. Jefferson, M. S. W. Beach Cusps. Abstract of a paper presented 

before Boston Meeting of the Geological Soc. of America, 1909. Pub- 
lished only in temporary "List of Papers with Abstracts." 

18. Shaler, N. S. Beaches and Tidal Marshes of the Atlantic Coast. 

National Geogr. Monogr. I, 137-168, 1895. 

19. Jefferson, M. S. W. Beach Cusps. Jour, of Geol. VII, 246, 1899. 

20. Kemp, James F. Unpublished field notes. 

21. Wilson, A. W. G. Cuspate Forelands Along the Bay of Quinte. Jour. 

of Geol. XII, 122, 1904. 

22. Jefferson, M. S. W. Shore Phenomena on Lake Huron. Jour, of 

Geol. XI, 124, 1903. 

23. Shaler, N. S. Beaches and Tidal Marshes of the Atlantic Coast. 

National Geogr. Monogr. I, 164, 1895. 

24. Cornish, Vaughan. On Sea Beaches and Sand Banks. Geog. Jour. 

London. XI, 637, 1898. 

25. Jefferson, M.S.W. Beach Cusps. Jour, of Geol. VII, 237-246, 1899. 

26. Jefferson, M. S. W. Shore Phenomena on Lake Huron. Jour. 

of Geol. XI, 123-124, 1903. 
Jefferson, M. S. W. On the Lake Shore. Normal College News. 
Ill, 1905. 

27. Branner, J. O. The Origin of Beach Cusps. Jour, of Geol. VIII, 

481-484, 1900. 
-* 28. Wilson, A. W. G. Cuspate Forelands Along the Bay of Quinte. Jour, 
of Geol. XII, 122, 1904. 
29. Cornish, Vaughan. Progressive Waves in Rivers. Geog. Jour. 
London. XXIX, 23-31, 1907. 
'30. Russell, I. C. Geological History of Lake Lahontan. U. S. Geol. 
Surv., Mon. XI, 92-93, 1885. 

31. Desor, E. On the Superficial Deposits of the District. In Report on 

the Geology of the Lake Superior Land District, by J. W. Foster 
and J. D. Whitney. Pt. 2, p. 258, Washington, 1851. 

32. Whittlesey, Charles. Freshwater Glacial Drift of the Northwestern 

States. Smithsonian Contribution No. 197, p. 17, Washington, 1866. 
* 33. Andrews, Edmund. The North American Lakes Considered as Chro- 
nometers of Post Glacial Time. Trans. Chicago Acad. Sci. II, 14, 
1870. 



REFERENCES 527 

34. Gilbert, G. K. The Topographic Features of Lake Shores. U. S. 

Geol. Surv., 5th Ann. Rep., Ill, 1885. 

35. Gilbert, G. K. Lake Bonneville. U. S. Geol. Surv. Mon. I, 44, 

1890. 
» 36. Hagen, G. Handbuch der Wasserbaukunst. 3. Teil. Das Meer, 
Erster Band., p. 97, et seq., Berlin, 1863. 

37. Braun, G. Entwickelungsgeschichtliche Studien an Europaischen Flach- 

landskiisten und ihren Diinen. Veroff. Inst, fur Meerskunde u. s. w. 
XV, 89-91, Berlin, 1911. 

38. Lehmann, F. W. P. Das Kustengebiet Hinterpommerns. Zeit. der 

Gesells. fur Erdkunde zu Berlin. XIX, 391, 1884. 

39. Otto. Theodor. Der Darss und Zingst. Jahresb. der Geogr. Gesells. 

Greifswald. XIII, 393-403, 1913. 

40. Cornish, Vaughan. On Sea Beaches and Sand Banks. Geog. Jour. 

London. XI, 637, 1898. 
* 41. Wheeler, W. H. The Sea Coast: Destruction: Littoral Drift: Pro- 
tection, p. 41, London, 1902. 

42. Kemp, James F. Unpublished field notes. » 

43. Dodge, R. E. Continental Phenomena Illustrated by Ripple Marks. 

Science. XXIII, 38-39, 1894. 

44. Siau. De l'Action des Vagues a de Grandes Profondeurs. Comptes 

Rendus de l'Academie des Sciences. XII, 774-776, 1841. 
Siau. De Taction des Vagues a de Grandes Profondeurs. Annales de 
Chimie et de Physique, 3 e Ser. II, 118-120, 1841. 

45. Beche, H. T. de la. The Geological Observer, p. 506, Philadelphia, 

1851. 

46. Barrell, Joseph. Criteria for the Recognition of Ancient Delta De- 

posits. Bull. Geol. Soc. Amer. XXIII, 429, 1912. 

47. Sorby, H. C. On the Structure Produced by the Currents Present 

During the Deposition of Stratified Rocks. The Geologist, p. 141, 
1859. 

48. Gilbert, G. K. Ripple Marks. Bull. Philosophical Society of Wash- 

ington. II, 61-62, 1875. 

49. Hunt, A. R, On the Formation of Ripplemark. Proc. Roy. Soc, 

London. XXXIV, 2, 18, 1882. 

50. Hunt, A. R. The Descriptive Nomenclature of Ripple-Mark. Geo- 

logical Mag., N. S., 5th Dec. I, 411, 1904. 

51. Hunt, A. R. On the Action of Waves on Sea-Beaches and Sea-Bottoms. 

Proc. Roy. Dublin Soc, N. S. IV, 261-262, 1884. 

52. Hunt, A. R. The Descriptive Nomenclature of Ripple-Mark. Geo- 

logical Mag. N. S., 5th Dec I, 410-418, 1904. 

53. Hunt, A. R. Facts Observed by Lieut. Damant, R. N., at the Sea- 

bottom. Geol. Mag., N. S., Dec. 5. V, 31-33, 1908. 

54. Candolle, C. de. Rides Formees a la Surface du Sable Depose au 

Fond de l'Eau et Autres Phenomenes Analogues. Archives des 
Sciences Physiques et Naturelles, 3 e Ser. IX, 241-278, 1883. 

55. Forel, F. A. Les Rides de Fond Etudiees dans le Lac Leman. Ar- 

chives des Sciences Physiques et Naturelles, 3 e Ser. X, 39-72, 1883. 



528 MINOR SHORE FORMS 

56. Forel, F. A. [La formation des rides du limon.] Bull, de la Societe 

Vaudoise des Sciences Naturelles. X, 518, 1870. 
Forel, F. A. Les Rides de Fond. Bull, de la Soci6te Vaudoise des 

Sciences Naturelles. XV, P. V, 66-68, 1878. 
Forel, F. A. [Les rides de fond dans le Golfe de Morgues.] Bull, de 

la Societe Vaudoise des Sciences Naturelles. XV, P. V, 76-77, 1878. 

57. Forel, F. A [La formation des rides du limon.] Bull, de la Societe 

Vaudoise des Sciences Naturelles. X, 518, 1870. 
Forel, F. A. Les Rides de Fond Etudiees dans le Lac Leman. Ar- 
chives des Sciences Physiques et Naturelles, 3 e Ser. X, 40, 1883. 

58. Darwin, G. H. On the Formation of Ripple Mark in Sand. Roy. 

Soc. of London, Proc. XXXVI, 18-43, 1883. 

59. Ayrton, H. The Origin and Growth of Ripple Mark. Proc. Roy. 

Soc. London, Ser. A, LXXXIV, 285-310, 1910. 

60. Reynolds, Osborne. Report of the Committee Appointed to In- 

vestigate the Action of Waves and Currents on the Beds and Fore- 
shores of Estuaries by Means of Working Models. Rept. of the 
Brit. Assoc, for 1889, pp. 327-343, 1889. 

Reynolds, Osborne. Report of the Committee Appointed to Investi- 
gate the Action of Waves and Currents on the Beds and Foreshores 
of Estuaries by Means of Working Models. Report of the British 
Assoc, for 1890, pp. 512-534, 1890. 

Reynolds, Osborne. Report of the Committee Appointed to Investi- 
gate the Action of Waves and Currents on the Beds and Foreshores 
of Estuaries by Means of Working Models. Rept. of the British 
Assoc, for 1891, pp. 386-404, 1891. 
6i. Reynolds, Osborne. Report of the Committee Appointed to In- 
vestigate the Action of Waves and Currents on the Beds and Fore- 
shores of Estuaries by Means of Working Models. Rept. of the 
British Assoc, for 1889, p 343, 1889. 

62. Cornish, Vaughan. On Tidal Sand Ripples above Low-water Mark. 
/ Rept. of British Assoc, for 1900, pp. 733-734, 1900. 

63. Cornish, Vaughan. Sand Waves in Tidal Currents. Geog. Jour. 

London. XVIII, 170-202, 1901. 
Cornish, Vaughan. On the Formation of Wave Surfaces in Sand. 
Scottish Geog. Mag. XVII, 1-11, 1901. 

64. Cornish, Vaughan. On Tidal Sand Ripples above Low-water Mark. 

Rept. of British Assoc, for 1900, p. 733, 1900. 
Cornish, Vaughan. Sand Waves in Tidal Currents. Geog. Jour. 

London, XVIII, 197-198, 1901. 
Cornish, Vaughan. On the Formation of Wave Surfaces in Sand. 

Scottish Geog. Mag., XVII, 8, 1901. 

65. Cornish, Vaughan. Waves of Sand and Snow, pp. 289-290, Lon- 

don, 1914. 

66. Gilmore, John. Storm Warriors, or Lifeboat Work on the Goodwin 

Sands, pp. 108-109, London, 1874. 

67. Kindle, E. M. Recent and Fossil Ripple Mark. Canadian Geol. 

Survey, Museum Bull. Mo. 25, pp. 19, 22, 1917. 



REFERENCES 529 

68. Ibid., p. 32. 

69. Ibid., p. 20. 

70. Pierce, Raymond, C. The Measurement of Silt-Laden Streams. 

U. S. Geol. Surv. Water Supply Paper 400-C, p. 20, 1916. 

71. Reynolds, Osborne. Report of the Committee Appointed to Investi- 

gate the Action of Waves and Currents on the Beds and Foreshores 
of Estuaries by Means of Working Models. Rept. of the Brit. Assoc, 
for 1889, p. 343, 1889. 

72. Gilbert, G. K. Ripple-marks and Cross-dedding. Bull. Geol. Soc. 

Amer. X, 135-140, 1899. 

73. Fairchild, H. L. Beach Structure in the Medina Sandstone. Amer. 

Geologist. XXVIII, 9-14, 1901. 

74. Branner, J. C. Editorial Note. Jour, of Geol. IX, 535-536, 1901. 

75. Owens, John S. Experiments on the Transporting Power of Sea 

Currents. Geog. Jour. London. XXXI, 415-425, 1908. 
78. Brown, A. P. The Formation of Ripple-Marks, Tracks and Trails. 
Proc. Acad. Nat. Sci., Philadelphia. LXIII, 536-547, 1911. 

77. Epry, Ch. Les Ripple-Marks. Annales de lTnstitut Oceanographique. 

IV, Fascicule 3, 1-16, 1912. 

78. Cornish, Vaughan. On Kumatology. Geog. Jour., London. XIII, 

624-628, 1899. 
Cornish, Vaughan. Waves of Sand and Snow, p. 278, London, 1914. 

79. Owens, John S. Experiments on the Transporting Power of Sea 

Currents. Geog. Jour., London. XXXI, 424, 1908. 

80. Gilbert, G. K. The Transportation of Debris by Running Water. 

U. S. Geol. Surv. Professional Paper 86, p. 11, 1914. 

81. Pierce, Raymond, C. The Measurement of Silt-Laden Streams. 

U. S. Geol. Surv. Water Supply Paper 400-C, p. 42, 1916. 

82. Kindle, E. M. Recent and Fossil Ripple Mark. Canadian Geol. 

Survey, Museum. Bull. No. 25, pp. 1-56, 1917. 

83. Ibid., p. 27. 

Kindle, E. M. Recent and Fossil Ripple Mark. Canadian Geol. 
Survey, Museum. Bull. No. 25, 48, 1917. 

84. Ibid., p. 48. 

85. Hyde, Jesse E. The Ripples of the Bedford and Berea Formations 

of Central and Southern Ohio, with Notes on the Paleogeography of 
that Epoch. Jour, of Geol. XIX, 257-269, 1911. 

86. Bucher, Walter H. Large Current Ripples as Indicators of Paleoge- 

ography. Nat. Acad. Sci., Proc. Ill, 285-291, 1917. 

87. Scrope, G. P. On the Rippled Markings of Many of the Forest Marble 

Beds North of Bath, and the Foot-tracks of Certain Animals Occur- 
ring in Great Abundance on their Surfaces. Proc. Geol. Soc, Lon- 
don. I, 317-318, 1831. 

88. Darwin, G. H. In the Geological Importance of the Tides. Nature. 

XXV, 214, 1882. 

89. Van Hise, C. R. Principles of North American Pre-Cambrian Geology. 

U. S. Geol. Surv., 16 th Ann. Rept. Pt. I, 719-721, 1896. 

90. Gilbert, G. K. Ripple Marks. Science. Ill, 376, 1884. 



530 MINOR SHORE FORMS 

91. Spurr, J. E. False Bedding in Stratified Drift Deposits. Amer. 

Geol. XIII, 43-47, 1894. 

92. Jaggar, T. A., Jr. Some Conditions of Ripple Mark. Amer. Geol. 

XIII, 199-201, 1894. 

93. Spurr, J. E. Oscillation and Single Current Ripple Marks. Amer. 

Geol. XIII, 201-206, 1894. 

94. Sorby, H. C. On the Application of Quantitative Methods to the 

Study of the Structure and History of Rocks. Quart. Jour. Geol. 
Soc, London. LXIV, 180-185, 1908. 

95. Ibid., pp. 181, 197-199. 

96. Locke, John. Professor Locke's Geological Report. Geol. Surv. of 

Ohio, 2nd Ann. Rept., p. 246, 1838. 

97. Foerste, A. F. On Clinton Conglomerates and Wave Marks in Ohio 

and Kentucky. Jour, of Geol. Ill, 193-194, 1895. 
Foerste, A. F. The Richmond Group along the Western Side of 
the Cincinnati Anticline in Indiana and Kentucky. Amer. Geol. 
XXXI, 356, 1903. 

98. Gilbert, G. K. Ripple Marks. Science. Ill, 375-376, 1884. 

99. Moore, Joseph and Hole, A. D. Concerning Well-defined Ripple 

Marks in Hudson River Limestone, Richmond, Indiana. Indiana 
Acad. Science, Proc. for 1900, pp. 216-220, 1901. 

100. Cushing, H. P. Geology of the Vicinity of Little Falls. New York 

State Museum, Bull. 77, p. 34, 1905. 

101. Miller, W. J. Geology of the Port Leyden Quadrangle. N. Y. State 

Museum, Bull. 135, p. 36, 1910. 

102. Kindle, E. M. and Taylor, F. B. Description of the Niagara Quad- 

rangle. U. S. Geol. Surv. Folio 190, p. 7, 1913. 

103. Udden, J. A. Notes on Ripple Marks. Jour, of Geol. XXIV, 

123-129, 1916. 

104. Prosser, C. S. Ripple Marks in Ohio Limestones. Jour, of Geol. 

XXIV, 456-475, 1916. 

105. Wooster, L. C. Ripple Marks in Limestone. Science. Ill, 274, 1884. 

106. Kindle, E. M. A Comparison of the Cambrian and Ordovician Ripple- 

Marks Found at Ottawa, Canada. Jour, of Geol. XXII, 712, 1914. 

107. Udden, J. A. Notes on Ripple Marks. Jour, of Geol. XXIV, 125, 1916. 

108. Kindle, E. M. Note on a Ripple-Marked Limestone. Ottawa Nat- 

uralist. XXVI, 108-110, 1913. 
Kindle, E. M. A Comparison of the Cambrian and Ordovician Ripple- 
Marks Found at Ottawa, Canada. Jour, of Geol. XXII, 711, 1914. 

109. Shannon, W. P. Wave Marks on Cincinnati Limestone. Indiana 

Acad. Science, Proc. for 1894, pp. 53-54, 1895. 

110. Johnson, Douglas W. Contributions to the Study of Ripple Marks. 

Jour, oi Geol. XXIV, 809-819, 1916. 

111. Nathorst, A. G. Om Nagra formodade vaxtfossilier. Ofversigt of 

Kongl. Vet. Akad. Forhandl. XXX, 25-52, 1874. 

112. Nathorst, A. G. Om Spar af nagra evertebrerade djur m. m. och 

deras paleontologiska betydelse. Handlingar Kongl. Svenska Vet. 
Akad. XVIII (1880), 1-104, 1881. 



REFERENCES 531 

113. Saporta, G. de. A Propos des Algues Fossiles. Paris, 1882. 
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Relatif aux Algues Fossiles. Bull. Soc. Geol. de France, 3 e Ser. XI, 
159-162, 1883. 

Saporta, G. de. Les Organismes Problematiques des Anciens Mers. 
100 pp., Paris, 1884. 

Saporta, G. de. Nouveaux Documents Relatif s a des Fossiles Vege- 
taux et a des Traces d'Invertebres Associes dans les Anciens Ter- 
rains. Bull. Soc. Geol. de France, 3 e Ser. XIV, 407-430, 1886. 

114. Nathorst, A. G. Quelques Remarques Concernants la Question des 

Algues Fossiles. Bull. Soc. Geol. de France, 3 e Ser. XI, 452-455, 
1883. 
Nathorst, A. G. Nouvelles Observations sur des Traces d'Animaux 
et Autres Phenomenes d'Origine Purement Mecanique Decrits comme 
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115. Gaudry, A. Note sur l'Ouvrage de M. le Marquis de Saporta Inti- 

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116. Williamson, W. C. On Some Undescribed Tracks of Invertebrate 

Animals from the Yoredale Rocks, and on some Inorganic Phenomena, 
Produced on Tidal Shores, Simulating Plant Remains. Memoirs 
Manchester Literary and Philosophical Society, 3rd Ser. X, 19-29, 
1887. 

117. Dodge, R. E. Continental Phenomena Illustrated by Ripple Marks. 

Science. XXIII, 38-39, 1894. 

118. Jaggar, T. A., Jr. Experiments Illustrating Erosion and Sedimen- 

tation. Bull. Mus. Comp. Zool. XLIX, 285-305, 1908. 

119. Grabau, A. W. Principles of Stratigraphy, p. 708, New York, 

1913. 

120. Fairchild, H. L. Beach Structure in the Medina Sandstone. Amer. 

Geol. XXVIII, 14, 1901. 

121. Williamson, W. C. On Some Undescribed Tracks of Invertebrate 

Animals from the Yoredale Rocks, and on some Inorganic Phenomena, 
Produced on Tidal Shores, Simulating Plant Remains. Memoirs 
Manchester Literary and Philosophical Society, 3rd Ser., X, 25, 1887. 

122. Kindle, E. M. Recent and Fossil Ripple Mark. Canadian Geol. 

Survey, Museum. Bull., No. 25, p. 34, 1917. 

123. Sokolow, N. A. Die Dunen: Bildung, Entwickelung und Innerer 

Bau, pp. 38-40, Berlin, 1894. 
Beaurain, G. Quelques Faits Relatifs a la Formation du Littoral des 
Landes de Gascogne Revue de Geogr. XXVIII, 255-260, 1891. 

124. Sokolow, N. A. Die Dunen: Bildung, . Entwickelung und Innerer 

Bau, pp. 42-44, Berlin, 1894. 
Berendt, G. Geologie des Kiirischen Haffes und seiner Umgebung, 
pp. 83-95, Konigsberg, 1869. 

125. Merrill, F. J. H. Barrier Beaches of the Atlantic Coast. Pop. Sci. 

Mon. XXXVII, 736-745, 1890. 



532 MINOR SHORE FORMS 

126. Latrobe, B. H. Memoir on the Sand Hills of Cape Henry in Virginia. 

Am. Jour. Sci. 2d Ser. XL, 261-264, 1865. Reprinted from Trans. 
Am. Phil. Soc. IV, 439-444. 

127. Cobb, Collier. The Forms of Sand Dunes as Influenced by Neigh- 

boring Forests. Elisha Mitchell Scientific Society Jour. XX, 14, 

1904. 
Cobb, Collier. Notes on the Geology of Corrituck Banks. Elisha 

Mitchell Scientific Society, Jour. XXII, 17-19, 1906. 
Cobb, Collier. Where the Wind does the Work. Nat. Geog. Mag. 

XVII, 310-317, 1906. 

128. Bremontier, N. T. Memoire sur les Dunes Annales des Ponts et 

Chaussees. I, 145-224, 1833. 

129. Solger, F., et al. Diinenbuch. 404 pp. Stuttgart, 1910. 

130. Sokolow, N. A. Die Dlinen; Bildung, Entwickelung und Innerer 

Bau. 298 pp., Berlin, 1894. 

131. Ibid., pp. 45-47. 



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Bache, A. D. On the Tidal Currents of New York Harbor near Sandy Hook. 

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Bailey, L. W. Notes on the Geology and Botany of Digby Neck. Nova 

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533 



534 LIST OF AUTHORITIES 

Barnes, H. T. Report on the Influence of Icebergs and Land on the Tem- 
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qBarre, O. Origines Tectonique du Golfe de Saint-Malo. Ann. Geog., XIV, 
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Barrell, Joseph. Relative Geological Importance of Continental, Littoral, 
and Marine Sedimentation. Journal of Geology, XIV, 316-356, 430-457, 
1906. 
q Barrell, Joseph. Criteria for the Recognition oF Ancient Delta Deposits. 
Bull. Geol. Soc. Amer., XXIII, 377-446, 1912. 

Barrell, Joseph. Piedmont Terraces of the Northern Appalachians and 
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Bazin, Henri. Recherches Experimentales sur la Propagation des Ondes. 
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Beaufort, Francis. Karamania, or a Brief Description of the South Coast 
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r> Beaumont, Elie de. [La derniere limite en profondeur des traces de 1 'agita- 
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Beaumont, Elie de. Lecons de Geologie Pratique. 557 pp., Paris, 1845. 

Beaurain, G. Quelques Faits Relatifs a la Formation du Littoral des Landes 
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Beazeley, A. The Reclamation of Land from Tidal Waters. 314 pp., 
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OBeche, Henry T. de la. Researches in Theoretical Geology. 408 pp., 
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■ >Beche, Henry T. de la. The Geological Observer. 695,'pp., Philadelphia, 1851. 

Berendt, G. Geologie des Kurischen Haffes und seiner Umgebung. 110 
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Berghaus, Heinrich. Die Ersten Elemente der Erdbeschreibung. Berlin, 
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Bertin, Emile. Donnees Theoriques et Experimentales sur les Vagues et le 
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Bertin, Emile. Etude sur la Houle et le Roulis. Memoires de la Societe 
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Bjerknes, V. and Sandstrom, J. W. Uber die Darstellung des Hydrographi- 
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Bois, Coupvent des. Memoire sur la Hauteur des Vagues a la Surface des 
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Boussinesq, J. Essai sur la Theorie des Eaux Courantes. M6m. de l'Acad. 
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Branner, J. C. The Poror6ca, or Bore, of the Amazon. Science, IV, 488- 

492, 1884. 

1 Branner, J. C. The Origin of Beach Cusps. Jour. Geology, VIII, 481-484, 

1900. 
Branner, J. C. Editorial Note. Jour. Geology, IX, 535-536, 1901. 



LIST OF AUTHORITIES 535 

Branner, J. C. The Stone Reefs of Brazil; their Geological and Geographi- 
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Zool., XLIV, 1-285, 1904. 
Branner, J. C. Stone Reefs on the Northeast Coast of Brazil. Bull. Geol 

Soc. Amer., XVI, 1-12, 1905. 
Braun, Gustav. Einige Ergebnisse Entwickelungsgeschichtlicher Studien 
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r Gesellschaft fur Erdkunde zu Berlin, 543-560, 1911. 
Braun, Gustav. Entwicklungsgeschichtliche Studien an Europaischen 

Flachlandskiisten und ihren Dunen. Veroff. Inst, fiir Meereskunde u. s. w., 

XV, 1-174, Berlin, 1911. 
Bremontier, N. T. Recherches sur le Mouvement des Ondes. 122 pp., 

Paris, 1809. 
Brigham, A. P. The Fiords of Norway. Bull. Amer. Geog. Soc, XXXVIII, 

337-348, 1906. 
Brogger, W. C. tiber die Bildungsgeschichte des Kristianiafjords, Ein 

Beitrag zum Verstandniss der Fjord- und Seebildung in Skandinavien, 

Nyt. Mag. Nat., XXX, 99-231, 1886. 
Brown, A. P. The Formation of Ripple-marks, Tracks and Trails. Proc. 

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Brown, Robert. On the Formation of Fjords, Canons, Benches, Prairies, 

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O Brown, Robert. Remarks on the Formation of Fjords and Canons. Jour. 

Royal Geog. Soc, XLI, 348-360, 1871. 
Browne, W. R. The Relative Value of Tidal and Upland Waters in Main- 
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LXVI, 1-85, 1881. 
- Bryson, John. [On the beaches along the southern side of Long Island.] 

American Geologist, II, 64-65, 1888. 
Bryson, John. The So-called Sand Dunes of East Hampton, L. I. American 

Geologist, VIII, 188-190, 1891. 
Buchan, Alexander. Specific Gravities and Oceanic Circulation. Trans. 

Roy. Soc Edinburgh, XXXVIII, 317-342, 1897. 
Buchanan, G. Y. The Guinea and Equatorial Currents. Geographical 

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Burrows, Montagu. Cinque Ports, 2nd Edition. 261 pp., London, 1888. 

O Caligny, A. de. Oscillations de l'Eau. 964 pp., Paris, 1883. 
Candolle, C. de. Rides Formees a la Surface du Sable Depose au Fond de 
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Carpenter, W. B. Ocean Circulation. Contemporary Review, XXVI, 
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O Cialdi, Alessandro. Sul Moto Ondoso del Mare e su le Correnti di esso. 
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• Clapp, C. H. Contraposed Shorelines. Jour. Geology, XXI, 537-540, 1913. 



536 LIST OF AUTHORITIES 

Cobb, Collier. The Forms of Sand Dunes as Influenced by Neighboring 
Forests. Elisha Mitchell Sci. Soc. Jour., XX, 14, 1904. 

Cobb, Collier. Notes on the Geology of Currituck Banks. Elisha Mitchell 
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Cobb, Co lier. Where the Wind does the Work. Nat. Geog. Mag., XVII, 
pp. 310-317, 1906. 

Cold, Conrad. Kusten-Veranderungen im Archipel. 67 pp., Marburg, 
1886. 

Comstock, F. N. An Example of Wave Formed Cusp at Lake George, N. Y. 
Amer. Geologist, XXV, 192-194, 1900. 

Coode, John. Description of the Chesil Bank, with Remarks upon its 
Origin, the Causes which have Contributed to its Formation, and upon the 
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1853. 

Coode, John. [On depth of wave action.] Min. Proc. Inst. C. E., LXX, 
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OCook, George H. On a Subsidence of the Land on the Sea-coast of New 
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1857. 
O Cook, George H. The Change of Relative Level of the Ocean and the 
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O Cornaglia, P. Sul Regime delle Spiagge e sulla Regolazione dei Porti. Re- 
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Cornish, Vaughan. On Sea Beaches and Sand Banks. Geog. Jour. Lon- 
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O Cornish, Vaughan. On Kumatology. Geog. Journal, XIII, 624-628, 1899. 

Cornish, Vaughan. On Tidal Sand Ripples above Low-water Mark. Rept. 
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* Cornish, Vaughan. Sand Waves in Tidal Currents. Geog. Jour. London, 

XVIII, 170-202, 1901. 
■ Cornish, Vaughan. On the Formation of Wave Surfaces in Sand. Scottish 

Geog. Mag., XVII, 1-11, 1901. 
Cornish, Vaughan. On the Dimensions of Deep Sea Waves, and their 

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London, XXIII, 623-645, 1904. 
Cornish, Vaughan. Progressive Waves in Rivers. Geog. Jour. London, 

XXIX, 23-31, 1907. 
Cornish, Vaughan. Waves of the Sea and Other Water Waves. 374 pp., 

Chicago, 1911. 
O Cornish, Vaughan. On the Principles which Govern the Transportation 

of Sand and Shingle by Tides and Waves, with a Note on the Severn Bore. 

Jour. Roy. Soc. of Arts, LX, 1121-1126, 1912. 
•Cornish, Vaughan. Waves of Sand and Snow. 383 pp., London, 1914. 

* Cotton, C. A. Fault Coasts in New Zealand. The Geographical Review, I, 

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Cronander, A. W. On the Laws of Movement of Sea-currents and Rivers. 
57 pp., appendices, Norrkoping, 1898. 



LIST OF AUTHORITIES 537 

Crosby, W. O. A Study of the Geology of the Charles River Estuary and 
Boston Harbor, with Special Reference to the Building of the Proposed 
Dam across the Tidal Portion of the River. Technology Quarterly, XVI, 
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Cubitt, Wm. [On shingle fulls.] Min. Proc. Inst. Civ. Eng., XI, 205, 
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Cushing, H. P. Geology of the Vicinity of Little Falls. New York State 
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Cushing, S. W. The East Coast of India. Bull. Amer. Geogr. Soc. XLV, 
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Cushing, S. W. Personal communication. 

Dall, W. H. Harbors of Alaska and the Tides and Currents in their Vicinity. 

U. S. Coast Survey, Rept. for 1872, pp. 177-212, 1875. 
Daly, R. A. The Geology of the Northeast Coast of Labrador. Bull. Mus. 

Comp. Zool., XXXVIII, Geol. Ser. V, pp. 205-270, 1902. 
Daly, R. A. Pleistocene Glaciation and the Coral Reef Problem. Amer. 

Jour. Sci., XXX, 297-308, 1910. 
Daly, R. A. The Glacial-Control Theory of Coral Reefs. Proc. Amer. 

Acad. Arts and Sci., LI, 157-251, 1915. 
Daly, R. A. Problems of the Pacific Islands. Amer. Jour. Sci., XLI, 153- 

186, 1916. 
Dana, J. D. Geology, U. S. Exploring Expedition during the years 1838 to 

1842, under the command of Charles Wilkes, X, 756 pp., 1849. 
O.Dana, J. D. Manual of Geology. 798 pp., Philadelphia, 1863. 

Dana, J. D. Corals and Coral Islands. 398 pp., New York, 1872. 
O Dana, J. D. Manual of Geology. 4th Edition, 1088 pp., New York, 

1895. 
Darwin, G. H. On the Formation of Ripple-mark in Sand. Royal Society 

of London, Proc, XXXVI, 18-43, 1883. 
Darwin, G. H. On the Geological Importance of the Tides. Nature, XXV, 

213-214, 1882. 
Darwin, G. H. The Tides and Kindred Phenomena in the Solar System. 

342 pp., London, 1898. 
fe Davis, Chas. A. Salt Marsh Formation near Boston and its Geological 

Significance. Economic Geology, V, 623-639, 1910. 
Davis, Chas,. A. Some Evidences of Recent Subsidence on the New England 

Coast. Abstract Science new ser., XXXII, 63, 1910. 
Davis, Chas. A. Salt Marshes, A Study in Correlation. Abstract: Assoc. 

Am. Geographers Annals, I, 139-143, 1911. 
Davis, C. H. A Memoir upon the Geological Action of the Tidal and Other 

Currents of the Ocean. Mem. Amer. Acad. Arts and Sciences, N. S., IV., 

Reprint, 40 pp., 1849. 
Davis, W. M. Topographic Development of the Triassic Formation of the 

Connecticut Valley. Amer. Jour. Sci., 3rd Ser., XXXVII, 423-434, 1889. 
O Davis, W. M. and Wood, J. W. The Geographic Development of Northern 

New Jersey. Proc. Bost. Soc. Nat. Hist., XXIV, 365-423, 1890. 
Davis, W. M. Physical Geography. 432 pp., Boston, 1898. 



538 LIST OF AUTHORITIES 

Davis, W. M. Geographical Essays. Edited by Douglas W. Johnson, 777 
pp., Boston, 1909. 

Davis, W. M. Die Erklarende Beschreibung der Landformen. 565 pp., 
Leipzig and Berlin, 1912. 

Davis, W. M. Meandering Valleys and Underfit Rivers. Assoc. Amer. 
Geographers, Annals, III, 3-28, 1913. 

Davis, W. M. Dana's Confirmation of Darwin's Theory of Coral Reefs. 
Amer. Jour. Sci., XXXV, 173-188, 1913. 

Davis, W. M. Home Study of Coral Reefs. Bull. Amer. Geogr. Soc. XLVI, 
561-577, 641-654, 721-739, 1914. 

Davis, W. M. Shaler TVIemorial Study of Coral Reefs. Amer. Jour. Sci., 
XL, 223-271, 1915. 

Davis, W. M. Problems Associated with the Origin of Coral Reefs. Scien- 
tific Monthly, II, 313-333, 479-501, 557-572, 1916. 

Dawson, J. W. Acadian Geology. Third Edition. 694 pp., and supp. 102 
pp., London, 1878. 

Dawson, W. Bell. Note on Secondary Undulations Recorded by Self- 
Registering Tide Gauges, and on Exceptional Tides in Relation to Wind 
and Barometer. Trans. Roy. Soc. Canada, I, Sec. 3, 25-27, 1895. 

Dawson, W. Bell. Report of Progress for the year 1894 in the Survey of 
Tides and Currents in Canadian Waters. Proc. Roy. Soc. Canada, I, 14- 
22, 1895. 

Dawson, W. Bell. Illustrations of Remarkable Secondary Tidal Undula- 
tions, in January 1899, as Registered on Recording Tide Gauges in the 
Region of Nova Scotia. Trans. Roy. Soc, Canada, 2nd Ser., V, Sec. Ill, 
23-26, 1899. 

Delesse, M. Lithologie des Mers de France, 479 + 136 pp., Paris, 1872. 

Desor, E. On the Superficial Deposits of the District. In Report on the 
Geology of the Lake Superior Land District, by J. W. Foster and J. D. 
Whitney, Part 2, 406 pp., Washington, 1851. 

Dinse, P. Die Fjordbildungen. Ein Beitrag zur Morphographie der Kusten. 
Zeitschrift der Gesellschaft fur Erdkunde zu Berlin, XXIX, 189-259, 
1894. 

Dodge, R. E. Continental Phenomena Illustrated by Ripple Marks. Science, 
XXIII, 38-39, 1894. 
O Douglas, J. N. [On the depth of wave action.] Min. Proc. Inst. Civ. Eng., 
XL, 103, 1875. 

Drew, F. [On the Dungeness], quoted by Wm. Topley in The Geology of 
the Weald. Mem. Geol. Surv. England and Wales, pp., 212-215, 302-312, 
1875. 
O Duane, J. C, et al. Report of Board of Engineers on Deepening Gedney's 
Channel through Sandy Hook Bar, New York. 48th Congress, 2nd Session, 
House of Representatives Executive Document No. 78, pp. 11-15, 1885. 

Dutton, C. E. The Tertiary History of the Grand Canyon District. U. S. 
Geol. Surv. Monograph, II, pp. 1-260, 1882. 

Ekman, F. L. On the General Causes of the Ocean Currents. Nova Acta 
Regiae Societatis Scientiarum Upsaliensis, Serie III, X, 52 pp., 1876. 



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Ekman, V. W. Ein Beitrag zur Erklarung und Berechnung des Strom ver- 

laufs an Flussmiindungen. Kongl. Vetenskaps-Akademiens Forhandlingar, 

pp. 479-507, 1899. 
Ekman, V. W. Beitrage zur Theorie d Meeresstromungen. Annalen der 

Hydrographie und Maritimen Meteorologie, XXXIV, 423-430, 472-484, 

527-540, 566-583, 1906. 
Ekman, V. W. On Dead Water. The Norwegian North Polar Expedition, 

1893-1896, Scientific Results, V, No. 15, 152 pp., Christiania, 1906. 
Emy, A. R. Du Mouvement des Ondes et des Travaux Hydrauliques Mari- 

times. 188 pp., Paris, 1831. 
OEpry, Ch. Les Ripple- Marks. Annales de PInstitut Oceanographique, IV, 

Fascicule 3, 1-16, 1912. 
Esmark, Jens. Remarks Tending to Explain the Geological History of the 

Earth. Edinburgh New Phil. Jour, for 1826, pp. 107-121, 1827. 

Fairchild, H. L. Beach Structure in the Medina Sandstone. Amer. Geol- 
ogist, XXVIII, 9-14, 1901. 

Fairchild, H. L. Ice Erosion Theory a Fallacy. Bull. Geol. Soc. Amer. 
XVI, 13-74, 1905. 

Fenneman, N. M. Development of the Profile of Equilibrium of the Sub- 
aqueous Shore Terrace. Jour, of Geol., X, 1-32, 1902. 

Fischer, Theobald. Zur Entwickelungsgeschichte der Kiisten. Petermanns 
Geographische Mitteilungen, XXXI, 409-420, 1885. 

Fischer, Theobald. Kiistenstudien aus Nordafrika. Petermanns Geo- 
graphische Mitteilungen, XXXIII, 1-13, 33-44, 1887. 

Fischer, Theobald. Kiistenstudien und Reiseeindrucke aus Algerien. 
Zeitschrift der Gesellschaft fur Erdkunde zu Berlin, pp. - 554-576, 
1906. 

Fischer, Theobald. Fenomeni di Abrasione sulle Coste dei Passi dell' 
Atlante. Rendiconti della R. Accademia dei Lincei, Roma, XVI, 571- 
575, 1907. 

Fleming, J. A. Waves and Ripples in Water, Air, and Aether. 299 pp., 
London, 1902. 

Fleming, Sanford. Toronto Harbor — Its Formation and Preservation. 
Canadian Journal, II, 105-107, 223-230, 1853. 

Foerste, A. F. On Clinton Conglomerates and Wave Marks in Ohio and 
Kentucky. Jour. Geology III, 50-60, 169-197, 1895. 

Foerste, A. F. The Richmond Group along the Western Side of the Cin- 
cinnati Anticline in Indiana and Kentucky. Amer. Geologist, XXXI, 333- 
361, 1903. 

Fol, Hermann. Les Impressions d'un Scaphandrier. Revue Scientifique, 
XLV, ,711-715, 1890. 

Forbes, Edward. Abrading Power of Water at Different Velocities. Proc. 
Roy. Soc. Edinburgh, III, 474-477, 1856-57. 

Forel, F. A. La Formation des Rides du Limon. Bulletin de la Soci6te 
Vandoise des Sciences Naturelles, X, 518, 1870. 

Forel, F. A. Les Rides de Fond. Bulletin de la SociSte" Vaudoise des 
Sciences Naturelles, XV, P. V, 66-68, 1878. 



540 LIST OF AUTHORITIES 

Forel, F. A. Les Rides de Fond dans le Golfe de Morgues. Bulletin de la 
Societe Vaudoise des Sciences Naturelles, XV, P. V, 76-77, 1878. 

Forel, F. A. Les Rides de Fond Etudiees dans le Lac Leman. Archives 
des Sciences Physiques et Naturelles, 3 L ' Ser., X, 39-72, 1883. 

Gaillard, D. D. Wave Action in Relation to Engineering Structures. 

Corps of Engineers, U. S. Army, Professional Paper XXXI, 232 pp., Wash- 
ington, 1904. 
Gallois, L. Les Andes de Patagonie. Annales de Geographie, X, 232-259, 

1901. 
Ganong, W. F. Notes on the Natural History and Physiography of New- 
Brunswick. N. B. Nat. Hist. Soc. Bull., XXVI, VI, pt. I, 17-39, 1908. 
Gardiner, J. Stanley. The Formation of the Maldives. London Geog. 

Jour., XIX, 277-296, 1902. 
Gaudry, A. Note sur l'Ouvrage de M. le Marquis de Saporta intitule: A 

Propos des Algues Fossiles. Bull. Soc. Geol. de France. 3 e Ser., XI, 156- 

158, 1883. 
Geikie, A. Textbook of Geology. 4th Edition, 2 Vols., 1472 pp., London, 

1903. 
Gilbert, G. K. Ripple Marks. Bull. Philosophical Society of Washington, 

II, 61-62, 1875. 
Gilbert, G. K. Ripple Marks. Science, III, 375-376, 1884. 
Gilbert, G. K. The Topographic Features of Lake Shores. 5th Ann. Rep. 

U. S. Geol. Surv., pp. 69-123, 1885. 
Gilbert, G. K. Lake Bonneville. U. S. Geol. Surv. Mon. I, 438 pp., 1890. 
Gilbert, G. K. Ripple Marks and Cross Bedding. Bull. Geol. Soc. Amer., 

X, 135-140, 1899. 
Gilbert, G. K. Glaciers and Glaciation. Harriman Alaska Expedition, III, 

1-231, 1904. 
Gilbert, G. K. The Transportation of Debris by Running Water. U. S. 

Geol. Surv. Professional paper 86, pp. 1-263, 1914. 
Gilmore, John. Storm Warriors, or Lifeboat Work on the Goodwin Sands. 

358 pp., London, 1874. 
Girard, Jules. La Geographie Littorale, 231 pp., Paris, 1895. 
Goldthwait, J. W. Supposed Evidences of Subsidence of the Coast of New 

Brunswick within Modern Time. Can. Geol. Surv. Museum Bulletin II, 

1-23 (of reprint), 1914. 
Grabau, A. W. Principles of Stratigraphy. 1185 pp., New York, 1913. 
Gre^n, A. H. Physical Geology. 2nd Edition, 555 pp., London, 1877. 
Gregory, H. E., Keller, A. G. and Bishop, A. L. Physical and Commercial 

Geography 469 pp., Boston, 1910. 
Gregory, J. W. The Nature and Origin of Fjords. 542 pp., London, 1913. 
Grossman, K. and Lomas, J. On the Glaciation of the Faroe Islands. Gla- 

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Gulliver, F. P. Cuspate Forelands. Bull. Geol. Soc. Amer., VII, 399-422, 

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Gulliver, F. P. Dungeness Foreland. London Geog. Jour. IX, 536-546, 

1897. 



LIST OF AUTHORITIES 541 

' Gulliver, F. P. Shoreline Topography. Proc. Amer. Acad.' Arts and 
Sciences, XXXIV, 151-258, 1899. 
Gurlt, F. A. tjber die Entstehungsweise der Fjorde. Sitz. Niederrheini- 
schen Ges. Natur-und Heilkunde, XXXI, 143-150, 1874. 
q Guttner, Paul. Geographische Homologien an den Kiisten mit besonderer 
Beriicksichtigung der Schwemmlandkusten, 59 pp., Leipzig, 1895. 

Haage, Reinhold. Die Deutsche Nordseekuste. 83 pp., Leipzig, 1899. 
Haast, J. von. Notes on the Causes which have led to th3 Excavation of 

Deep Lake-basins in Hard Rocks in the Southern Alps of New Zealand. 

Quart. Jour. Geol. Soc, XXI, 130-132, 1865. 
Hagen, G. Handbuch der Wasserbaukunst. 3. Teil. Das Meer. Erstet 

Band, 364 pp., Berlin, 1863. 
Hahn, F. G. Untersuchungen iiber das Aufsteigen und Sinken der Kiisten, 

223 pp., Leipzig, 1879. 
Hahn, F. G. Kusteneinteilung und Kustenentwickelung im verkehrs- 

geographischen Sinne. Verhandlungen des Deutschen Geographentages, 

VI, 99-117, 1886. 
OHallett, H. S. [On tidal scour.] Min. Proc. Inst. Civil Engrs., LXVI, 

54-55, 1881. 
Harrington, M. W. Surface Currents of the Great Lakes. Bull. B., U. S. 

Dept. Agriculture, Weather Bureau, 1895. 

* Harris, R. A. Manual of Tides, Part V. U. S. Coast Surv. Rept. for 1907, 

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* Harrison, J. T. Observations on the Causes that are in Constant Operation 

Tending to Alter the Outline of the English Coast, to Affect the Entrances 
of the Rivers and Harbours, and to Form Shoals and Deeps in the Bed of 
the Sea. Min. Proc. Inst. Civ. Eng., VII, 327-365, 1848. 

Haupt, L. M. Discussion on the Dynamic Action of the Ocean in Building 
Bars. Proc. Am. Phil. Soc, XXVI, 146-171, 1889. 

Helland, Amund. On the Ice-Fjords of North Greenland and on the For- 
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Jour. Geol. Soc, XXXIII, 142-176, 1877. 

Helland, Amund. Die Glaciale "Bildung der Fjorde und Alpenseen in Nor- 
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Helland-Hansen, Bjorn, and Nansen, Fridtjof. The Norwegian Sea. 
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Hentzschel, Otto. Die Hauptkiistentypen des Mittelmeers. 61 pp., Leip- 
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vHenwood, W. J. On the Metalliferous Deposits of Cornwall and Devon. 
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Hind, H. Y. Report on the Preservation and Improvement of Toronto 
Harbor. Canadian Journal, II, Supplement, 1-14, 1854. 

Hirt, Otto. Das Fjord-Problem. Jahresbericht des Konigl. Gymna- 
siums zu Soran, 12 pp., Soran, 1888. 

Hobbs, Wm. H. Origin of Ocean Basins in the Light of the New Seismology. 
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Hobbs, W. H. Earth Features and their Meaning. 506 pp., New York, 1912. 



542 LIST OF AUTHORITIES 

Howlett, B. S. [On beach-ridges.] Min. Proc. Inst. Civ. Eng., XI, 213, 1852. 
Hubbard, G. D. Fiords. Bull. Amer. Geog. Soc, XXXIII, 330-337, 401- 

408, 1901. 
Hull, Edward. The Physical History of the Norwegian Fjords. Geo- 
logical Magazine, Dec. 5, X, 9-11, 1916. 
Hunt, A. R. On the Formation of Ripple Mark. Proc. Roy. Soc. London, 

XXXIV, 1-18, 1882. 
Hunt, A. R. On the Action of Waves on Sea-Beaches and Sea-Bottoms. 

Proc. Roy. Dublin Soc. N. S., IV, 241-290, 1884. 
Hunt, A. R. The Formation and Erosion of Beaches. Nature, XLV, 415- 

416, 1892. 
Hunt, A. R. The Descriptive Nomenclature of Ripple Mark. Geological 

Magazine, N. S., Dec, 1, 410-418, 1904. 
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Lehmann, F. W. P. Das Kustengebiet Hinterpommerns. Zeitschrift der 

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•+ 



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O Mitchell, Henry. The Under-run of the Hudson River. U. S. Coast Sur- 
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Ratzel, Fr. Uber Fjordbildungen an Binnenseen; nebst Allgemeinen Be- 

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Reade, T. Mellard. Tidal Action as an Agent of Geological Change. 

Philosophical Magazine, XXV, 338-343, 1888. 
Reclus, Elise'e. The Ocean. 534 pp., New York, 1873. 
r Redman, John Baldry. The East Coast between the Thames and the Wash 

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Redman, John Baldry. On the Alluvial Formations and the Local Changes 

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Remmers, Otto. Untersuchungen der Fjorde an der Kuste von Maine, 63 

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Reusch, Hans. Some Contributions towards an Understanding of the 

Manner in which the Valleys and Mountains of Norway were Formed. 

Norges Geol. Undersog. Aarbog for 1900, pp. 239-263, 1901. 
Reusch, Hans. The Norway Coast Plain. Jour, of Geol., II, 347-349, 

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Reynolds, Osborne. Report of the Committee Appointed to Investigate 

the Action of Waves and Currents on the Beds and Foreshores of Estuaries 

by Means of Working Models. Report of the British Association for 1889, 

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Reynolds, Osborne. Report of the Committee Appointed to Investigate 

the Action of Waves and Currents on the Beds and Foreshores of Estuaries 

by Means of Working Models. Report of the British Association for 1890, 

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Reynolds, Osborne. Report of the Committee Appointed to Investigate 

the Action of Waves and Currents on the Beds and Foreshores of Estuaries 

by Means of Working Models. Rept. of the British Association for 1891, 

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Richter, E. Die Norwegische Strandebene und ihre Entstehung. Globus, 

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548 LIST OF AUTHORITIES 

Ritter, Carl. Uber Geographische Stellung und Horizontale Ausbreitung 
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Ritter, Carl. Bemerkungen uber Veranschaulichungsmittel Raumlicher 
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Robertson, W. A. Scott. The Cinque Ports Liberty of Romney. Archseo- 
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> Royal Commission on Coast Erosion. Minutes of Evidence. Reports of 
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Ruhl, Alfred. Beitrage zur Kenntnis der Morphologischen Wirkarbeit der 
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Russell, I. C. Geological History of Lake Lahontan. Mon. U. S. Geol. 
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Russell, J. Scott. Report of the Committee on Waves, Appointed by the 
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Russell, J. Scott. Report on Waves made to the Meetings in 1842 and 
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Russell, J. Scott. [On local changes of tide heights and on the character of 
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Russell, J. Scott. The Modern System of Naval Architecture. 3 Vols., 
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Salisbury, R. D. Physiography. 770 pp., New York, 1907. 
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Saporta, G. de. Les Organismes Problematiques des Anciens Mers. 100 

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ScHOTT, Arthur. Die Kiistenbildung des Nordlichen Yukatan. Pet. Geog. 

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Schott, Gerhard, tlber die Dimensionen der Meereswellen. "Festschrift 

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Schroter, Walter. Korea und die Riasverwandten Kiisten dieser Halb- 

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Schwind, Friedrich. Die Riaskusten und ihr Verhaltnis zu den Fjord- 

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Scott, W. B. An Introduction to Geology. 816 pp., New York, 1911. 
Scrope, G. P. On the Rippled Markings of Many of the Forest Marble Beds 

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Shaler, N. S. Preliminary Report on Sea Coast Swamps of the Eastern 

United States. U. S. Geol. Surv., 6th Ann. Rept., pp. 353-398, 1886. 
Shaler, N. S. The Geology of Cape Ann, Mass. U. S. Geol. Surv., 9th Ann. 

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Shaler, N. S. Note on the Value of Saliferous Deposits as Evidence of 

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* Shaler, N. S. Sea and Land. 252 pp., New York, 1894. 
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Shaler, N. S. Evidences as to Changes of Sealevel. Bull. Geol. Soc. Am. 

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Shannon, W. P. Wave Marks on Cincinnati Limestone. Indiana Acad. 

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Shield, William. Principles and Practice of Harbor Construction. 299 

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Siau. De l'Action de ; Vagues a de Grandes Profondeurs. Comptes Rendus 

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Siau. De l'Action des Vagues a de Grandes Profondeurs. Annales de Chimie 

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Sokolow, N. A. Die Diinen: Bildung, Entwickelung und Innerer Bau. 

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OSolger, F., et al. Dunenbuch. 404 pp., Stuttgart, 1910. 

Sollas, W. J. The Estuaries of the Severn and its Tributaries. Quart. 

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Sorby, H. C. On the Structures Produced by the Currents Present During 

the Deposition of Stratified Rocks. The Geologist, pp. 137-147, London, 1859. 
Sorby, H. C. On the Application of Quantitative Methods to the Study of 

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Spurr, J. E. Oscillation and Single Current Ripple Marks. Amer. Geol- 
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Spurr, J. E. False Bedding in Stratified Drift Deposits. Amer. Geologist, 

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Steffen, Hans,. Der Baker-Fiord in West-Patagonien. Pet. Geog. Mitt., 

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Stevenson, Robert. On the Bed of the German Ocean, or North Sea. 

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Stevenson, T. Account of Experiments upon the Force of the Waves of the 

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Stevenson, T. The Design and Construction of Harbours. 3rd Edition, 

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Stokes, George Gabriel. Report on Recent Researches in Hydrodynamics. 

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Stokes, George Gabriel. On the Theory of Oscillatory Waves. Mathe- 
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Suess, Eduard. Das Antlitz der Erde. I, 778 pp., Wien, 1892. 

Tarr, R. S. Wave-formed Cuspate Forelands. American Geologist, XXII, 

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Tarr, R. S. The Yakutat Bay Region, Alaska, Physiography and Glacial 

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O Taylor, Frank B. Personal ommunication. 

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in the Natural Currents of Lake Michigan. Document No. 762, 63rd 

Congress, 2nd Session, Appendix C, pp. 40-48, 1914. 

Udden, J. A. Notes on Ripple Marks. Journal of Geology, XXIV, 123- 
129, 1916. 

Upham, Warren. The Fiords and Great Lake Basins of North America 
Considered as Evidence of Pre-Glacial Continental Elevation and of Depres- 
sion during the Glacial Period. Bull. Geol. Soc. Amer., I, 563-567, 1890. 

Upham, Warren. Fjords and Hanging Valleys. Amer. Geologist, XXXV, 
312-315, 1905. 

Van Hise, C. R. Principles of North American Pre-Cambrian Geology. 

U. S. Geol. Surv., 16th Ann. Rept., Pt. I, 581-842, 1896. 
Vaughan, T. W. A Contribution to the Geologic History of the Floridian 

Plateau. Carnegie Institution. Papers from the Tortugas Laboratory, IV, 

99-185, 1910. 
Vaughan, T. W. Present Status of the Investigations of the Origin of Barrier 

Coral Reefs. Amer. Jour. Sci., XLI, 131-135, 1916. 
Vogt, J. H. L. Sondre Helgelands Morfologi. Norges Geol. Unders. No. 

29, pp. 1-61, 160-170, 1900. 
Vogt, J. H. L. Uber die Schrage Senkung und die Spiitere Schrage Hebung 

des Landes in Nordlichen Norwegen. Reprint from Norsk Geologisk 

Tidsskrift, I, 47 pp., 1907. 



LIST OF AUTHORITIES 551 

Weber, Ernst Heinrich and Wilhelm. Wellenlehre auf Experimente 

Gegriindet. 433 pp., Leipzig, 1825. 
Weidemuller, O. R. Die Schwemmlandkiisten der Vereinigten Staaten 

von Nordamerika. 58 pp., Leipzig, 1894. 
Werth, Emil. Fjorde, Fjarde, und Fohrden. Zeit. fur Gletscherkunde, III, 

346-358, 1909. 
Weule, Karl. Beitrage zur Morphologie der Flach-Kusten. Weimar Z. f. 

Wiss. Geog. VIII, 6-8, 211-256, 1891. 
Wharton, W. J. L. Foundations of Coral Atolls. Nature, LV, 390-393 

1897. 
Wheeler, W. H. The Sea Coast: Destruction; Littoral Drift; Protection. 

361 pp., London, 1902. 
Wheeler, W. H. A Practical Manual of Tides and Waves. 201 pp., Lon- 
don, 1906. 
Whewell, W. Report on Discussions of Bristol Tides, Performed by Mr. 

Bunt under the Direction of the Rev. W. Whewell. Report of the British 

Association, XI, 30-33, 1842. 
White, W. H. Manual of Naval Architecture. 5th Edition, 731 pp., Lon- 
don, 1900. 
Whittlesey, Charles. Freshwater Glacial Drift of the Northwestern 

States. Smithsonian Contribution No. 197, Washington, 1866. 
Williams, H. S. Geologic Biology. 395 pp., New York, 1895. 
Williamson, W. C. On Some Undescribed Tracks of Invertebrate Animals 

from the Yoredale Rocks, and on some Inorganic Phenomena, Produced on 

Tidal Shores, Simulating Plant Remains. Memoirs Manchester Literary 

and Philosophical Soc, 3rd. Ser., X, 19-29, 1887. 
Willis, Bailey. Conditions of Sedimentary Deposition. Jour. Geol., I, 

476-520, 1893. 
Wilson, A. W. G. Cuspate Forelands Along the Bay of Quinte. Jour. 

Geol., XII, 106-132, 1904. 
Wilson, A. W. G. Shoreline Studies on Lakes Ontario and Erie. Bull. Geol. 

Soc. Amer., XIX, 471-500, 1908. 
Woodman, J. E. Shore Development in the Bras d'Or Lakes. American 

Geologist, XXIV, 329-342, 1899. 
Wooster, L. C. Ripple Marks in Limestone. Science, III, 274, 1884. 
Wright, W. B. On a Preglacial Shoreline in the Western Isles of Scotland. 

Geol. Magazine N. S., Decade V, VIII, 97-109, 1911. 



INDEX — AUTHORS 



This part of the Index includes the names of all authorities mentioned 
throughout the book. 

Often, the name of the authority will not be found upon the page noted, 
— only the number of that authority in the table of References at the end of 
the chapter. 

Minor heads under names of authorities refer to general subjects treated, 
and not to titles of authors' works. These minor heads are the same as 
major heads under Index — Subjects. Under those major heads will be 
found the names of all the authorities upon the subjects. 



Abbe, C, 

Development of Shoreline — 
(Emergence) : 390, 394 (35) 
(Submergence) : 336, 347 QS) 
Abbe, C, Jr., 

Current Action: 140, 141, 156 (153) 
Development of Shoreline — 
(Emergence) : 383, 393 (27) 
Abercromby, R., 

Water Waves: 25, 50 (93) 
Agassiz, A., 

Current Action: 141, 156 (154) 
Minor Shore Forms: 462, 526 (10) 
Terminology and Classification of 

Shores: 189 
Work of Waves: 80, 85 (52) 
Agassiz, L., 

Development of Shoreline — 
(Emergence) : 350, 354, 392 (4) 
Airy, G. B., 

Current Action: 143, 144 
Water Waves: 3, 5, 12, 25, 29, 32, 
46 (8, 17), 48 (48), 50 (94), 51 
(114), 52 (123, 125) 
Work of Waves: 80, 85 (51) 
Anderson, J., 

Current Action: 136, 155 (137) 
Andrews, E., 

Current Action: 101, 149 (20) 
Development of Shore Profile : 228, 

269 (28) 
Minor Shore Forms: 486, 526 (33) 



Andrews, E. C. 

Terminology and Classification of 
Shores: 179, 196 (64, 68) 
Anonymous, 

Current Action: 122, 153 (82) 
Antoine, C, 

Water Waves: 29, 51 (111) 
Appach, F. H., 

Shore Ridges: 426, 455 (35) 
Austen, R. A. C, 

Current Action: 143 

Development of Shore Profile: 216, 
268 (8) 
Ayrton, H., 

Minor Shore Forms: 498, 528 (59) 



121, 140, 153 (75), 
33, 52 (129) 



Bache, A. D., 
Current Action: 

156 (151) 
Water Waves: 
Bailey, L. W., 

Current Action: 107, 150 
Barnes, H. T., 

Current Action: 132, 155 
Barrell, J., 

Development of Shoreline — 
(Neutral and Compound): 397, 
403 (2) 
Minor Shore Forms: 491, 527 (46) 
Terminology and Classification of 
Shores: 161, 165, 168, 193 
(6, 9, 21) 



553 



554 



INDEX — AUTHORS 



Bazin, H., 

Water Waves: 5, 18, 46 (16), 49 
(63) 
Beaufort, F., 

Development of Shoreline — 
(Submergence) : 309, 346 (18) 
Beaumont, E. De, 

Development of Shoreline — 

(Emergence) : 351, 354, 355, 356, 
358, 359, 365, 393 (9) 
Development of Shore Profile : 260, 
271 (82) 
Beaurain, G., 

Minor Shore Forms: 519, 531 



Shore Ridges: 442, 456 (58) 
Beazeley, A., 

Current Action: 111, 151 (48) 
Beche, H. T. De La, 

Development of Shoreline — 
(Submergence): 272, 345 (1) 

Minor Shore Forms: 491, 527 (45) 
Belcher, E., 

Current Action: 143 
Berendt, G., 

Minor Shore Forms: 519, 531 (124) 
Berghaus, H. 

Terminology and Classification of 
Shores: 170, 194 (36) 
Bertin, E., 

Water Waves: 5, 47- (21, 22) 
Bishop, A. L., Gregory, H. E., 
Keller, A. G. and, 

Terminology and Classification of 
Shores: 168, 194 (23) 
Bjerknes, V. and Sandstrom, J. W., 

Current Action: 134, 155 (129) 
Bois, C. Des, 

Water Waves: 23, 28, 50 (80), 51 
(106) 

BOUSSINESQ, J., 

Water Waves: 5, 47 (20) 
Branner, J. C, 

Current Action: 109, 119, 138, 

151 (47), 152 (73), 156 (143) 
Development of Shoreline — 
(Submergence): 308, 309, 346 
(17) 



Branner, J. C. (continued), 

Minor Shore Forms: 460, 461, 462, 
475, 478, 501, 525 (7, 8), 526 
(27), 529 (74) 
Braun, G., 

Minor Shore Forms: 487, 527 (37) 
Shore Ridges: 422, 430, 455 (22) 
Bremontier, N. T., 

Current Action: 104, 150 (24) 
Minor Shore Forms: 519, 532 

(128) 
Water Waves: 4, 11, 46 (11), 48 (46) 
Brigham, A. P., 

Terminology and Classification of 
Shores: 181, 196 (74) 
Brogger, W. C, 
Terminology and Classification of 
Shores: 179, 196 (62) 
Brown, A. P., 

Minor Shore Forms: 501, 502, 529 
(76) 
Brown, R., 

Terminology and Classification of 
Shores: 181, 197 (81) 
Browne, A. J. Jukes-; see Jukes- 
Browne, A. J. 
Browne, W. R., 

Current Action: 113, 115, 119, 151 
(49), 152 (55, 61, 69) 
Bruckner, 

Shore Ridges: 411, 435, 437, 438 
Bryson, J., 

Development of Shoreline — 
(Emergence): 350, 392 (1, 2) 
Buchan, A., 

Current Action: 124, 136, 142, 
153 (90), 155 (139), 157 (161) 
Buchanan, G. Y., 

Current Action: 124, 153 (89) 
Buchanan, J. Y., 

Current Action: 139, 156 (150) 
Bucher, W. H., 

Minor Shore Forms: 508, 529 (86) 
Bunt, 

Current Action: 130, 154 (113) 
Burrows, M., 

Shore Ridges: 424, 426, 455 (32, 
36) 



INDEX — AUTHORS 



555 



Caligny, A. De, 

Current Action: 93, 149 (15) 
Water Waves: 3, 5, 6, 11, 32, 36, 

47 (26), 48 (45), 52 (127, 136) 
Calver, E. K., 

Work of Waves: 77, 85 (36) 
Candolle, C. De, 

Minor Shore Forms: 494, 495, 496, 
497, 498, 500, 509, 527 (54) 
Carpenter, W. B., 

Current Action: 128, 154 (106) 
Case, G. O., Owens, J. S. and, 

Current Action: 97, 149 (17) 
Cialdi, A., 

Water Waves: 4, 5, 10, 18, 47 (25), 

48 (38, 42), 49 (67) 
Work of Waves: 80, 85 (53) 

Clapp, C. H., 

Development of Shoreline — ■ 
(Neutral and Compound): 401, 
403 (4) 
Cobb, C, 

Minor Shore Forms: 519, 532 (127) 
Cold, C, 

Current Action: 123, 153 (83) 
Development of Shoreline — 

(Submergence) : 309, 346 (19) 
Terminology and Classification of 
Shores: 190, 198 (105) 
Comstock, F. N., 

Development of Shoreline — ■ 
(Submergence) : 335, 347 (39) 
Conte, J. Le; see Le Conte, J. 
Coode, J., 

Current Action: 144, 157 (170, 

178), 158 (183) 
Development of Shore Profile : 217, 

219, 268 (10, 13) 
Work of Waves: 77, 80, 85 (37, 48) 

CORNAGLIA, P., 

Current Action: 91, 103, 149 (6), 

150 (22) 
Water Waves: 10, 48 (43) 
Cornish, V., 

Current Action: 89, 91, 107, 119, 

120, 121, 139, 149 (1, 7, 9), 

150 (28), 152 (66), 153 (74, 

77), 156 (1 45) 



Cornish, V. (continued), 

Minor Shore Forms: 460, 477, 

481, 488, 500, 501, 502, 525 (5), 

526 (24, 29), 527 (40), 528 

(62, 63, 64, 65), 529 (78) 

Shore Ridges: 411, 443, 455 (17), 

457 (60) 
Water Waves: 3, 6, 12, 15, 18, 21, 
22, 24, 25, 26, 27, 28, 29, 46 (3, 
7), 47 (31), 48 (50), 49 (59, 65, 
72, 73, 75, 77), 50 (81, 83, 
85, 87, 88, 89, 90), 51 (96, 97, 
103, 104, 107, 109, 110, 112) 
Work of Waves: 80, 82, 85 (50), 
86 (62, 63) 
Cotton, C. A., 

Development of Shoreline — 
(Neutral and Compound): 397, 
403 (3) 
Terminology and Classification of 
Shores: 189, 191, 198 (104,106) 
Credner, G. R., 

Development of Shoreline — 

(Neutral and Compound) : 395, 
403 (1) 
Cronander, A. W., 

Current Action: 139, 142, 156 
(147), 157 (165) 
Crosby, W. O., 

Current Action: 113,119,151(51), 
152 (67) 

CUBITT, \7., 

Shore Ridges: 411, 455 (16) 

CUSHING, H. P., 

Minor Shore Forms: 509, 530 (100) 

ClJSHING, S. W., 

Development of Shore Profile : 230, 
231, 270 (42, 43) 

Dall, W. H., 

Current Action: 137, 141, 155(141, 

157) 
Daly, R. A., 

Development of Shore Profile : 230, 

269 (34) 
Terminology and Classification of 

Shores: 179, 189, 196 (67), 

198 (102) 



556 



INDEX — AUTHORS 



Dam ant, Lt., 

Minor Shore Forms: 495 
Dana, J. D., 

Current Action: 108, 126, 130, 145, 
151 {39), 154 (100, 110), 158 

(184) 

Development of Shoreline — 

(Submergence) : 272, 345 (2) 
Terminology and Classification of 
Shores: 167, 174, 181, 189, 

193 (11), 195 (54), 196 (72) 
Darcy, 

Water Waves: 5, 46 (16) 
Darwin, G. H., 

Minor Shore Forms: 495, 497, 498, 

508; 528 (58), 529 (88) 
Terminology and Classification: 

174, 189 
Water Waves: 43, 54 (163) 
Darwin, L., 

Water Waves: 28, 51 (107) 
Da Vinci, L.; see Vinci, L. da 
Davis, C. A., 

Development of Shoreline — 
(Emergence): 351, 354, 385, 
393 (31) 
Davis, C. H., 

Current Action: 105, 150 (25) 
Davis, W. M., 

Development of Shoreline — 
(Submergence): 278, 281, 295, 
337, 339, 345 (3, 4, 9), 347 (44, 
46) 
Development of Shore Profile : 203, 
223, 235, 245, 246, 247, 248, 
249, 253, 254, 256, 257, 258, 
260, 268 (1), 270 (59), 271 (66, 
67, 68, 69, 71, 72, 76, 77, 78, 
79, 80, 83, 85) 
Shore Ridges: 405, 407, 408, 411, 

454 (.9,9), 455 (13) 
Terminology and Classification of 
Shores: 164, 167, 168, 169, 
172, 189, 193 (14, 19, 21, 22), 

194 (25, 26), 195 (51, 53), 
198 (101) 

Work of Waves: 75 



Davis, W. M. and Wood, J. W., 
Terminology and Classification of 
Shores: 168, 194 (24) 
Dawson, J. W., 

Current Action: 113,114,151(55). 
152 (59, 60) 
Dawson, W. B., 

Current Action: 130, 133, 154 

(115), 155 (124) 
Water Waves: 43, 54 (162) 
Delesse, M., 

Work of Waves: 80, 85 (49) 
Des Bois, C; see Bois, C. des. 
Desor, E., 

Minor Shore Forms: 486, 488, 526 
(31) 
Dinse, P., 

Terminology and Classification of 
Shores: 181, 184, 196 (77), 
197 (98) 
Dodge, R. E., 

Minor Shore Forms: 489, 513, 527 
(43), 531 (117) 
Douglas, J. N., 
Current Action: 143 
Work of Waves: 79, 85 (43) 
Drew, F., 

Shore Ridges: 404, 422, 424, 
426, 454 (2). 455 (25, 26, 27, 
33) 
Duane, J. C, et al., 

Development of Shoreline — 
(Submergence): 300, 346 (11) 
Dutton, C. E., 

Terminology and Classification of 
Shores: 167, 193 (17) 

Ekman, F. L., 

Current Action: 128, 130, 131, 
133, 134, 138, 139, 142, 154 
(105, 114, 116, 117), 155 (121, 
127), 156 (144, 146), 167 (160, 
161, 163) 
Ekman, V. W., 

Current Action: 89, 139, 149 (2), 
156 (148, 149) 

Water Waves: 44, 54 (166) 

Work of Waves: 56, 83 (2) 



INDEX — AUTHORS 



557 



Emy, A. R., 

Water Waves: 4, 10, 11, 46 (13), 
48 (41, 47) 
Epry, C, 

Minor Shore Forms: 502, 529 (77) 

ESMARK, J., 

Terminology and Classification of 
Shores: 179, 195 (59) 
Ewart, F. C, 

Development of Shoreline — 
(Submergence): 313 

Fairchild, H. L. 

Minor Shore Forms: 501, 517, 529 

(73), 531 (120) 
Terminology and Classification of 
Shores: 181, 197 (80) 
Fenneman, N. M., 

Development of Shore Profile: 211, 
220, 224, 235, 268 (2, 14), 269 
(0, 270 (61) 
Water Waves: 13, 48 (52) 
Fischer, T., 

Current Action: 135, 155 (131) 
Development of Shore Profile : 216, 
230, 268 (5), 269 (29, 30, 
31) 
Terminology and Classification of 
Shores: 169, 176, 190, 194 
(30), 195 (57), 198 (105) 
Fleming, J. A., 

Water Waves: 3, 6, 8, 12, 29, 30, 
46 (2, 4), 47 (28, 35), 48 (48), 
51 (115), 52 (119) 
Work of Waves: 56, 83 (1) 
Fleming, S., 

Current Action: 97, 149 (18) 
Development of Shoreline — 
(Submergence): 292, 322, 345 
(8), 346 (26) 

FOERSTE, A. F., 

Minor Shore Forms: 509, 530 (97) 
Forel, F. A., 

Minor Shore Forms: 494, 495, 496, 
497, 498, 512, 527 (55), 528 
(56, 57) 
Forbes, E., 
Work of Waves: 82, 86 (59) 



Fol, H., 

Work of Waves: 77, 85 (38) 

Gaillard, D. D., 

Current Action: 93, 106, 126, 149 

(12), 150 (27), 153 (96) 
Water Waves: 6, 13, 15, 20, 22, 23, 
24, 25, 26, 27, 30, 31, 32, 38, 
W (33), 4& (53,55), & (58,71, 
74), 50 (79, 84, 92, 95), 51 
(98, 99), 52 (117, 121, 122), 
53 (153) 
Work of Waves: 56, 57, 62, 63, 
68, 83 (2, 3, 4), 84 (9, 10,11, 
12, 18,21) 
Gallois, L., 

Terminology and Classification of 
Shores: 182, 197 (86) 
Gannett, 

Terminology and Classification of 
Shores: 179 
Ganong, W. F., 

Development of Shoreline — 
(Emergence): 351, 354, 387, 
392 (7), 394 (33) 
Shore Ridges: 446 
Gardiner, J. S., 

Current Action: 109, 151 (46) 
Gaudry, A., 

Minor Shore Forms: 513, 531 (1 15) 
Geikie, A., 

Current Action: 138, 144, 156 

(142), 157 (177) 
Development of Shore Profile: 249, 

250, 271 (73, 74) 
Work of Waves: 68, 80, 84 (19, 
22), 85 (51) 
Gerstner, F., 

Water Waves: 4 
Gibbs, J., 

Current Action: 144 
Gilbert, G. K., 

Development of Shoreline — 

(Emergence) : 352, 354, 355, 356, 

357, 358, 360, 365, 376, 393 

(11, 13, 14, 16) 

(Submergence): 287, 310, 322, 

336, 345 (5), 346 (20), 347 (40 



558 



INDEX — AUTHORS 



Gilbert, G. K. (continued), 

Development of Shore Profile : 259, 

260, 271 (81, 84) 
Minor Shore Forms: 486, 488, 

494, 500, 501, 502, 508, 509, 

527 (34, 48), 529 (72, 80, 90), 

530 (98) 
Shore Ridges: 405, 407, 408, 411, 

454 (7, 8, 12) 
Terminology and Classification of 

Shores: 162, 163, 181, 193 

(7), 196 (69) 
Work of Waves: 69,84 (23) 

GlLMORE, J., 

Minor Shore Forms: 500, 528 (66) 

GOLDTHWAIT, J. W., 

Development of Shoreline — 
(Emergence): 351, 392 (8) 
Shore Ridges: 442, 446, 456 (56, 
59), 457 (61) 
Grabau, A. W., 

Current Action: 124, 127, 128, 130, 
134, 136, 153 (87), 154 (110), 
155 (125, 130), 156 (140) 
Minor Shore Forms: 513, 531 
{119) 
Green, A. H., 

Development of Shore Profile: 235, 

270 (57) 
Terminology and Classification of 
Shores: 176, 195 (55) 
Gregory, H. E., Keller, A. G. and 
Bishop, A. L., 
Terminology and Classification of 
Shores: 168, 194 (23) 
Gregory, J. W., 

Terminology and Classification of 
Shores: 167, 182, 193 (12), 
197 (93) 
Grossman, K. and Lomas, J., 
Terminology and Classification of 
Shores: 181, 196 (78) 
Gulliver, F. P., 

Current Action: 140, 141, 156 

(152, 154) 
Development of Shoreline — 
(Emergence): 376, 381, 382, 383, 
393 (22, 25, 28) 



Gulliver, F. P. (continued), 

(Submergence): 291, 303, 308, 
311, 315, 322, 324, 328, 329, 
332, 333, 334, 339, 345 (6), 
346 (12, 16,21, 23, 27, 28, 29, 
30, 31), 347 (32, 33, 34, 45) 

Development of Shore Profile : 225, 
226, 235, 269 (23, 25), 270 (60) 

Shore Ridges: 404, 424, 426, 454 
(4), 455 (28, 30, 34) 

Terminology and Classification of 
Shores: 159, 161, 164, 165, 
172,173, 192 (1, 3), 193 (5, 8), 
195 (52) 
Gurlt, F. A., 

Terminology and Classification of 
Shores: 182, 197 (89) 

GUTTNER, P., 

Terminology and Classification of 
Shores: 171, 181, 195 (48), 
197 (83) 

Haage, R., 

Development of Shore Profile: 234, 

270 (55) 
Terminology and Classification of 
Shores: 169, 194 (32) 
Haast, J. VON, 

Terminology and Classification of 
Shores: 179, 195 (60) 
Hagen, G., 

Minor Shore Forms: 487, 527 (36) 
Water Waves: 3, 18, 49 (61) 
Work on Waves: 57, 83 (5) 
Hahn, F. G., 

Development of Shore Profile: 234, 

270 (54) 
Terminology and Classification of 
Shores: 169, 171, 194 (31, 41) 
Hallet, H. S., 

Current Action: 108, 109, 151 (43) 
Hansen; see Helland-Hansen, B. 
Harrington, M. W., 

Current Action: 123, 126, 153 (85), 
154 (99) 
Harris, R. A., 

Current Action: 108, 121, 122, 125, 
127, 128, 133, 135, 136, 140, 



INDEX — AUTHORS 



559 



142, 145, 151 (36), 153 (76, 78, 
92, 93), 154 (101, 102, 103, 
'l04.), 155 (122, 123, 133, 135, 
140), 156 (151, 158), 157 (166), 
158 (186) 
Water Waves: 43, 53 (16 >) 
Harrison, J. T., 

Current Action: 107, 150 (28) 
Work of Waves: 75, 85 (35) 
Haupt, L. M., 

Current Action: 99, 149 (19) 
Water Waves: 42, 53 (156) 
Helland, A., 

Terminology and Classification of 
Shores: 179, 195 (61), 196 (61) 
Helland-Hansen, B., 

Current Action: 109, 135, 151 (44), 

155 (134-) 
Development of Shore Profile : 230 
Helland-Hansen, B. and Hansen, F. 
Current Action: 89, 90, 149 (3, 4) 
Water Waves: 44, 45, 54 (165, 167) 
Hentzschel, O., 

Development of Shoreline — 

(Submergence): 306 ; 346 (14) 
Terminology and Classification of 
Shores: 171, 190, 195 (47), 
198 (105) 
Henwood, W. J., 

Work of Waves: 71, 84 (31) 
Hind, H. Y., 

Development of Shoreline — 
(Submergence) : 292, 345 (7) 

HlRT, O., 

Terminology and Classification of 
Shores: 181, 196 (76) 
Hise, C. R. van; see Van Hise, C. R. 
Hitchcock, 

Minor Shore Forms: 508 
Hjort, J., Murray, J. and, 

Current Action: 89, 109, 135, 136, 
141, 149 (3), 151 (44), 155 
(134, 126), 156 (156) 
Iobbs, W. H., 
Development of Shoreline — 
(Submergence): 318, 346 (25) 
Terminology and Classification 
of Shores: 182, 197 (88) 



Hobbs, W. H. (continued), 

Water Waves: 38, 53 (139) 
Hole, A. D., Moore, J. and, 

Minor Shore Forms: 509, 530 (99) 
Howlett, B. S., 

Shore Ridges: 411, 455 (15) 
Hubbard, G. D., 

Terminology and Classification of 
Shores: 179, 184, 196 (66), 
197 (99) 
Hull, E., 

Terminology and Classification of 
Shores: 181, 196 (75) 
Hunt, A. R., 

Current Action: 124, 142, 144, 153 

(88), 157 (164, 169) 
Development of Shore Profile: 216, 

268 (3, 7) 
Minor Shore Forms: 494, 495, 527 

(49, 50, 51, 52, 53) 
Water Waves: 36, 52 (137) 
Work of Waves: 77, 82, 85 (39) 
Hunt. E. B., 

Current Action: 141, 156 (154) 
Hyde, J. E., 

Minor Shore Forms: 505, 529 (85) 



Jagger, T. A., Jr., 

Minor Shore Forms: 509, 513, 530 
(92), 531 (118) 
Jefferson, M. S. W., 

Minor Shore Forms: 460, 462, 463, 
467, 469, 470, 475, 477, 478, 
481, 525 (6, 9), 526 (12, 15, 
16, 17, 19, 22, 25, 26) 
Johnson, D. W., 

Development of Shore Profile : 224, 

269 (20), 247, 271 (70) 
Minor Shore Forms: 463, 510, 526 

(13), 530 (110) 
Terminology and Classification of 
Shores: 182, 197 (94) 
Johnson, D. W. and Reed, W. G., 
Development of Shoreline — 

(Submergence): 295, 318, 346 
(10, 24) 
Development of Shore Profile: 223, 
268 (18) 



560 



INDEX — AUTHORS 



Johnson, D. W. and Reed, W. G. 
(continued), 
Shore Ridges: 412, 451, 455 (21), 
457 (62) 
Jukes-Browne, A. J., 

Development of Shore Profile: 235, 

270 (58) 
Terminology and Classification of 
Shores: 176, 195 (55) 

Kayser, E., 

Development of Shore Profile : 234, 
270 (52) 
Keilhack, K., 

Shore Ridges: 404, 411, 431, 433, 
435, 436, 437, 438, 440, 442, 
454 (6), 455 (20), 456 (42, 44, 
45, 48, 49, 50, 51, 53, 54, 57) 
Keller, A. G. and Bishop, A. L., 
Gregory, H. E., 
Terminology and Classification of 
Shores: 168, 194 (23) 
Kelvin, Lord, 

Water Waves: 3, 8, 46 (1), 47 (35) 
Kemp, J. F., 

Minor Shore Forms: 466, 471, 488, 
526 (14, 20), 527 (42) 
Kinahan, G. H., 

Current Action: 93, 105, 108, 144, 149 

(13), 150(26), 151(37), 158(181) 

Development of Shore Profile: 216, 

268 (6) 
Work of Waves: 79,85 (44) 
Kinahan, H. C, 

Current Action: 108, 151 (38) 
Kindle, E. M., 

Minor Shore Forms: 500, 501, 504, 

505, 508, 517, 528 (67), 529 

(68, 69, 82, 83, 84), 530 (106, 

108), 531 (122) 

Kindle, E. M. and Taylor, F. B., 

Minor Shore Forms: 509, 530 (102) 

Kloden, 

Terminology and Classification of 
Shores: 170 

KORNERUP, A., 

Terminology and Classification of 
Shores: 182, 197 (91) 



Kruger, G., 

Current Action: 126, 153 (97) 

Shore Ridges: 437, 438, 456 (52) 
Krummel, O., 

Current Action: 94, 107, 108, 109, 
122, 129, 136, 150 (28, 30), 
151 (35, 40, 45), 153 (80), 
154 (107), 156 (140) 

Water Waves: 3, 6, 15, 18, 20, 32, 
33, 35, 38, 39, 40, 41, 42, 43, 
46 (10), 47 (32), 49 (60, 69, 
70), 52 (128, 129, 134), 53 
(140, 145, 147, 148, 149, 150, 
151, 152, 153, 158, 159) 

Lagrange, 

Water Waves: 32, 52 (126) 
Lane, A. C, 

Minor Shore Forms: 458, 476, 
525 (2) 
Lapparent, A. De, 

Development of Shore Profile: 234, 

270 (50, 51) 
Terminology and Classification of 
Shores: 167, 182, 193 (18), 
197 (85) 
Work of Waves: 82, 86 (61) 
Latrobe, B. H., 

Minor Shore Forms: 519, 532 
(126) 
Lawson, A. C, 

Development of Shore Profile : 228, 

269 (27) 
Terminology and Classification of 
Shores: 167, 193 (13) 
Le Conte, J., 

Current Action: 138, 156 (143) 
Terminology and Classification of 
Shores: 176, 182, 195 (58), 
197 (87) 
Lehmann, F. W. P., 

Minor Shore Forms: 487, 527 (38) 
Lewin, T., 

Shore Ridges: 424, 455 (31) 
Lindenkohl, A., 

Current Action: 123, 125, 135, 
153 (84, 91), 165 (135) 



INDEX — AUTHORS 



561 



Livingston, A. A., 

Development of Shoreline — 
(Submergence): 313 
Locke, J., 

Minor Shore Forms: 509, 530 (96) 
Loesche, Pechuel-; see Pechuel- 

Loesche. 
Lomas, J., Grossman,. K. and, 
Terminology and Classification of 
Shores: 181, 196 (78) 
Lyell, C, 

Minor Shore Forms: 497 
Work of Waves: 69, 71, 82, 84 (24, 
26) 
Lyman, C. S., 

Water Waves: 8, 48 (86) 

Marindin, H. L., 
Development of Shore Profile: 223, 
268 (17) 
Marinelli, O., 

Development of Shoreline — 
(Submergence): 311 
Marsh, G. P., 

Water Waves: 42, 53 (157) 
Marshall, P., 
Terminology and Classification of 
Shores: 181, 196 (70) 
Marten, H. J., 

Current Action: 113, 151 (49) 
Martonne, E. De., 

Development of Shore Profile : 234, 

270 (49) 
Terminology and Classification of 
Shores: 170, 171, 194 (40), 
195 (44) 
Marvine, A. R., 
Terminology and Classification of 
Shores: 167, 193 (15) 
Matthews, E. R., 

Current Action: 144, 157 (179) 
Work of Waves: 71, 84 (25, 27) 
Maury, M. F., 

Current Action: 135, 155 (132) 
McGee, W. J., 

Development of Shoreline — 
(Emergence) : 351, 354, 387, 388, 
392 (6), 394 (32, 34) 



Meinhold, F., 
Terminology and Classification of 
Shores: 169, 194 (34) 
Merrill, B. M., 

Development of Shoreline — 
(Emergence) : 356, 370 
Merrill, F. J. H., 

Development of Shoreline — 

(Emergence) : 350, 354, 392 (5) 
Minor Shore Forms: 519, 531 (125) 
Meunier, S., 

Work of Waves: 66, 84 (16) 
Mill, H. R., 

Current Action: 142, 157 (159) 
Miller, W. J., 

Minor Shore Forms: 509, 530 (101) 
Mitchell, H., 

Current Action: 113, 119, 126, 
145, 146, 151 (52), 152 (66, 68, 
70, 71), 153 (95), 158 (185) 
Development of Shore Profile: 237, 
270 (62) 
Moller, 

Water Waves: 32, 52 (128) 
Moore, J. and Hole, A. D., 
Minor Shore Forms: 509, 530 (99) 

MOTTEZ, A., 

Water Waves: 5, 28, 47 (24) 
Mudge, B. F., 
Development of Shoreline — 
(Emergence): 385, 393 (30) 
Murray, J., 

Current Action: 93, 149 (11) 
Development of Shore Profile: 216, 

268 (4) 
Terminology and Classification of 

Shores: 189 
Work of Waves: 81, 85 (37, 55), 86 

(56) 
Murray, J. and Hjort, J., et at., 
Current Action: 89, 109, 135, 136, 

141, 149 (3), 151 (44), 155 

(134, 136), 156 (156) 
Terminology and Classification of 

Shores: 189 

Nagel, C. H., 

Terminology and Classification: 
170, 194 (37) 



562 



INDEX — AUTHORS 



Nansen, F., 

Development of Shore Profile: 230, 
231, 270 (38, 41, 44, 45, 46) 
Work of Waves: 81,85 {55) 
Nansen, F., Helland-Hansen, B. 
and 
Current Action: 89, 90, 149 (3, 4) 
Water Waves: 44, 45, 54 (165, 167) 
Nares, Capt., 

Current Action: 136, 155 (138) 
Nathorst, A. G., 

Minor Shore Forms: 513, 530 
(111, 112), 531 (114) 
Newton, 

Water Waves: 4 
Nordenskjold. O., 

Terminology and Classification of 
Shores: 182, 197 (95) 

NUSSBAUM, F., 

Development of Shore Profile: 230, 
270 (40) 

Oldham, J., 

Current Action: 111, 151 (48) 
Otto, T., 

Current Action: 134, 142, 155 

(126), 157 (167) 
Development of Shore Profile : 223, 

269 (19) 
Minor Shore Forms: 487, 527 (39) 
Shore Ridges: 404, 430, 435, 454 
(5), 456 (39,40, 41,46,47) 
Owens, J. S., 

Minor Shore Forms: 501, 502, 529 
(75, 79) 
Owens, J. S. and Case, G. O., 
Current Action: 97, 149 (17) 

Palmer, H. R., 

Current Action: 96, 144, 149 (16), 

157 (174), 158 (182) 
Minor Shore Forms: 458, 525 (1) 
Paris, A., 

Water Waves: 27, 28, 51 (100, 109) 
Parsons, H. De B., 

Current Action: 107, 117, 122, 142, 
150 (31), 152 (62), 153 (79), 
157 (162) 



Passarge, S., 

Terminology and Classification of 
Shores: 167, 193 (20) 
Pechtjel-Loesche, 

Current Action: 129, 154 (109) 
Penck, A., 

Terminology and Classification of 
Shores: 169, 181, 184, 194 
(29), 197 (84, 97) 
Pendleton, A. G., 

Development of Shore Profile: 217, 
268 (12) 
Perkins, F. W., 

Current Action: 141, 156 (155) 
Peschel, O., 

Terminology and Classification of 
Shores: 182, 197 (90) 
Petrocchi, 

Development of Shoreline — 
(Submergence): 313 
Petterson, O., 

Current Action: 132, 134, 154 
(118), 155 (118, 128) 
Philippson, A., 

Current Action: 94 
Philippson, S., 

Development of Shoreline — 
(Submergence) : 335, 347 (38) 
Pianigiani, O., 

Development of Shoreline — ■ 
(Submergence): 312, 346 (22) 
Pierce, R. C, 

Minor Shore Forms: 500, 504, 529 
(70, 81) 
Playfair, J., 

Terminology and Classification of 

Shores: 176, 184, 195 (56) 
Work of Waves: 68, 84 (20) 
Powell, J. W., 

Terminology and Classification of 
Shores: 167, 193 (16) 
Prestwich, J., 

Current Action: 144, 157 (171, 
172, 173, 175) 
Prosser, C. S., 

Minor Shore Forms: 509, 530 
(104) 



INDEX — AUTHORS 



563 



Ramsay, A. C, 

Development of Shore Profile: 234, 
235, 270 (56) 
Rance, De, 

Development of Shoreline — 
(Submergence): 335 
Rankine, W. J. M., 

Development of Shore Profile : 226, 

269 (24) 
Water Waves: 5, 13, 47 (19), 48 
(51) 
Ratzel, Fr., 
Terminology and Classification of 
Shores: 159, 170, 184, 193 (4), 
194 (39), 197 (100) 
Reade, T. I., 

Minor Shore Forms: 480 
Reade, T. M., 

Current Action: 108, 136, 144, 145, 
151 (41), 155 (137, 138), 158 
(18j) 
Reclus, E., 

Current Action: 122, 153 (81) 
Redfield, 

Water Waves: 24, 50 (82) 
Redman, J. B., 

Current Action: 144, 157 (171) 
Shore Ridges: 404, 411, 422, 424, 
454 (1, 3), 455 (14, 23, 24, 
29) 
Reed, W. G., Johnson, D. W. and 
Development of Shoreline — 
(Submergence): 295, 318, 346 
(10, 24) 
Development of Shore Profile : 223, 

268 (18) 
Shore Ridges: 412, 451, 455 (21), 
J 457 (62) 
Reid, H. F., 

Water Waves: 39, 53 (142) 
Remmers, O., 

Terminology and Classification of 
Shores: 181, 197 (82) 
Rendel, J. M., 

Current Action: 143 
Rennie, G., 

Current Action: 143 



Reusch, H., 

Development of Shore Profile: 230, 

268 (35) 

Terminology and Classification of 
Shores: 179, 196 (63) 
Reuschle, 

Terminology and Classification of 
Shores: 171, 195 (45) 
Reynolds, O., 

Minor Shore Forms: 498, 500, 501, 
528 (60, 61) 

RlCCHIERI, G., 

Development of Shoreline — ■ 
(Submergence): 311 
Richardson, 

Current Action: 108 
Richter, E., 

Development of Shore Profile : 230, 

269 (36) 
Richthofen, F. von, 

Development of Shoreline — 

(Submergence) : 306, 346 (13) 
Development of Shore Profile: 234, 

270 (47, 48) 
Terminology and Classification of 

Shores: 169, 173, 194 (28) 

RlESSEN, P., 

Terminology and Classification of 
Shores: 171, 194 (42) 

RlTTER, C, 

Terminology and Classification of 
Shores: 170, 194 (35) 
Robertson, W. A. S., 

Shore Ridges: 426, 456 (37) 
Robinson, 

Current Action: 93, 149 (12) 
Ross, 

Water Waves: 28, 51 (105) 
Royal Commission on Coast Ero- 
sion, 
Work of Waves: 71, 84 (28) 
Russell, I. C, 

Development of Shoreline — 

(Emergence): 352, 393 (12, 15) 
Minor Shore Forms: 486, 488, 526 
(30) 

RtJHL, A., 

Current Action: 129, 154 (108) 



564 



INDEX — AUTHORS 



Russell, J. S., 

Current Action: 93, 104, 106, 107, 
143, 149 (10), 150 (24, 28) 

Water Waves: 3, 4, 5, 8, 18, 32, 
33, 34, 35, 36, 37, 38, 39, 41, 
46 (5, 6, 9, 14, 15), 47 (35), 
49 (62, 64), 52 (124, 130, 131, 
132, 133), 53 (138, 141, 143, 
154) 

Saint-Venant, B. de, 

Water Waves: 5, 47 (23) 
Salisbury, R. D., 

Current Action: 119, 126, 130, 
152 (72), 154 (98, 110) 
Sandstrom, J. W., 

Current Action: 132, 155 (119) 

Water Waves: 44, 54 (164) 
Sandstrom, J. W., Bjerknes, V. and, 

Current Action: 134, 155 (129) 
Saporta, G. de, 

Minor Shore Forms: 513, 531 (113) 

SCHOTT, A., 

Development of Shoreline — 
(Emergence) : 350, 392 (3) 

SCHOTT, G., 

Water Waves: 27, 51 (101) 

SCHROTER, W., 

Terminology and Classification of 
Shores: 171, 195 (46) 

SCHWIND, F,, 

Terminology and Classification of 
Shores: 170, 171, 194 (38), 
195 (43) 

SCORESBY, W., 

Water Waves: 24, 28, 50 (86, 88), 
51 (108) 
Scott, W. B., 

Development of Shore Profile : 234, 
270 (53) 
Scrope, G. P., 

Minor Shore Forms: 508, 529 (87) 
Shaler, N. S., 

Current Action: 93, 103, 149 (14) 
Development of Shoreline — 

(Emergence): 351,354,355,380, 

393 (10, 19, 24) 
(Submergence) : 307, 335, 346 (15) 



Shaler, N. S. (continued), 

Development of Shore Profile : 261, 

271 (86) 
Minor Shore Forms: 459, 460, 469, 
476, 477, 481, 482, 525 (3, 4), 
526 (18, 23) 
Terminology and Classification of 

Shores: 179, 196 (65) 
Work of Waves: 71, 84 (29, 30) 
Shannon, W. P., 

Minor Shore Forms: 509, 530 (109) 
Shield, W., 

Current Action: 130, 144, 154 

(112), 158 (180) 
Development of Shore Profile: 217, 

268 (9) 
Work of Waves: 67, 80 
Siau, 

Minor Shore Forms: 489, 491, 494, 

497, 504, 527 (44) 
Work of Waves: 80, 85 (54) 
Skertchley, S. B. J., 

Current Action: 113, 114, 151 (50), 
152 (57, 58) 
Sokolow, N. A., 

Minor Shore Forms: 519, 523, 531 

(123, 124), 532 (130, 131) 
Shore Ridges: 442, 456 (58) 
Solger, F., et al., 

Minor Shore Forms: 519, 532 (129) 
Shore Ridges: 442, 455 (19), 456 (43) 

SOLLAS, W. J., 

Current Action: 107, 108, 113, 114, 
117, 151 (34, 42), 152 (54, 56, 
64) 

SORBY, H. C, 

Minor Shore Forms: 494, 509, 527 

(47) 
Work of Waves: 82, 86 (60) 
Spratt, 

Current Action: 144, 157 (176) 
Steffen, H., 

Terminology and Classification of 
Shores: 182, 197 (92) 
Stevenson, R., 

Development of Shore Profile : 237, 

271 (63) 
Work of Waves: 77, 79, 85 (40, 41) 



INDEX — AUTHORS 



565 



Stevenson, T., 

Current Action: 107, 126, 150 (33), 

153 (94) 
Water Waves: 6, 15, 18, 23, 24, 47 

(27), 48 (57), 49 (66), 50 (78, 

82) 
Work of Waves: 57, 62, 63, 65, 74, 

79, 83 ((5, 7), 84 (8, 13, 14, 15), 

85 (32, 33, 34, 36, 42) 
Stokes, G. G., 

Current Action: 90, 149 (5) 
Water Waves: 5, 9, 10, 13, 45, 46 

(18), 47 (18), 48 (37, 39, 40, 

56), 54 (168) 
Suess, E., 

Terminology and Classification of 

Shores: 169, 190, 194 (27) 

Tannek, Z. L., 

Water Waves: 25, 50 (92) 
Tarr, R. S., 

Development of Shoreline — 

(Submergence) : 334, 347 (35) 
Terminology and Classification of 
Shores: 181, 196 (71) 
Tayler, J. W., 

Terminology and Classification of 
Shores: 181, 197 (79) 
Taylor, F. B., 

Current Action: 123, 153 (86) 
Water Waves: 26 
Taylor, F. B., Kindle, F. M. and, 
Minor Shore Forms: 509 530 (102) 
Thompson, Sir W.; see Kelvin, Lord 
Thoulet, J., 

Current Action: 122, 153 (80) 
Water Waves: 11, 18, 39, 43, 48 
(44), 49 (68), 53 (146), 54 
(161) 
Work of Waves: 81, 86 (58) 
Townsend, C. McD., 

Current Action: 101, 150 (20) 

Udden, J. A., 

Minor Shore Forms: 509, 530 (103, 
107) 
Upham, W., 

Terminology and Classification of 
Shores: 181, 196 (73) 



Van Hise, C. R., 

Minor Shore Forms: 508, 529 (89) 
Vatjghan, T. W., 

Current Action: 141, 156 (154) 
Terminology and Classification ol 
Shores: 189, 198 (103) 
Vinci, L. da, 

Water Waves: 1, 4 
Vogt, J. H. L., 

Development of Shore Profile : 225, 

230, 269 (22, 37), 270 (39) 
Terminology and Classification of 
Shores: 166, 193 (10) 

Weber, E. H. and W., 

Water Waves: 4, i7 22, 39, 46 (12), 

49 (76), 53 (144) 
Work of Waves: 81, 86 (57) 
Weidemuller, C. R., 

Development of Shoreline — 
(Emergence) : 355, 393 (20) 
Terminology and Classification of 
Shores: 169, 171, 194 (34), 
195 (50) 
Werth, E., 

Terminology and Classification of 
Shores: 182, 197 (96) 
Weule, K., 

Terminology and Classification of 
Shores: 171, 195 (49) 
Wharton, W. J. L., 

Development of Shore Profile : 230, 
269 (32, 33) 
Wheeler, W. H., 

Current Action: 103, 104, 107, 117, 
118, 119, 126, 130, 142, 146, 
147, 150 (23, 24, 29), 152 (63, 
65, 66), 154 (97, 115), 157 
(168), 158 (187) 
Development of Shoreline — ■ 

(Submergence) : 335, 347 (40) 
Development of Shore Profile : 217, 

220, 268 (11, 15, 16) 
Minor Shore Forms: 488, 527 (41) 
Shore Ridges: 411, 442, 455 (18 f 

55) 
Terminology and Classification of 
Shores: 159, 192 (2) 



566 



INDEX — AUTHORS 



Wheeler, W. H. (continued), 

Water Waves: 4, 6, 35, 36, 37, 41, 
42, 47 (29, 30), 52 (184, 135), 
53 (150. 155) 
Workof Waves: 79, 80, 85(45, 46, 47) 
Whewell, W., 

Current Action: 130, 154 (113) 
White, D., 

Development of Shoreline — 
(Emergence) : 351, 354 
White, W. H., 

Water Waves: 6, 12, 13, 25, 27, 28, 
29, 30, 31, 47 (34), 48 (49, 54), 
50 (91), 51 (102, 105, 113), 52 
(116, 118, 120) 
Whittlesey, C, 

Minor Shore Forms: 486, 526 (32) 
Williams, H. S., 

Development of Shore Profile : 253, 
271 (75) 
Williamson, W. C, 

Minor Shore Forms: 513, 517, 531 
(116 } 121) 



Willis, B., 

Current Action: 130, 154 (111) 
Wilson, A. W. G., 

Current Action: 101, 150 (21) 
Development of Shoreline — 

(Submergence) : 335, 347 (37) 
Minor Shore Forms: 462, 463, 475, 
479, 480, 526 (11,21, 28) 
Wilson, J., 

Current Action: 143 
Wood, J. W., Davis, W. M. and, 
Terminology and Classification of 
Shores: 168, 194 (24) 
Woodman, J. E., 

Development of Shoreline — 
(Submergence) : 334, 347 (36) 

WOOSTER, L. C, 

Minor Shore Forms: 509, 530 

(105) 
Wright, W. B., 

Development of Shore Profile: 228, 

269 (26) 



INDEX — SUBJECTS 



This part of the Index is arranged by topics. No attempt has been 
made to include general or casual references. 

All heads have been based upon the chapter heads, the topical heads, and 
the sub-topical heads of the book itself. At the end of those heads that are 
the same as the minor heads of the Index — Authors, special reference will 
be found to the authorities upon the subjects. 



Abrasion, marine, theory re, 234 

platform, 162, 225 
Aeolian denudation, 166-169 

peneplane, 166-169 

plain, 164-169 

plane, 166-169 
Alluvial outwash plain, 263 

plain, 188 
Appach's map, of ridges, 426 
Asymmetrical ripples, 494-512 
see also Ripple marks 

Backshore, 161 
terrace, 163 

see also Terraces 
Backwash, 517 

see also Marks 
Balls and lows, 486-489 
paraUel balls, 487-488 

see also Shore forms, minor 
Baltic sea, dunes of the, 519-524 
Barrier, 352 

see also Bars 
Barrier-bar, 352 
see also Bars 
Barrier-beach, 259 

see also Beaches 
Bars, 300-403 
barrier-bar, 352 
bay bar, 300, 351 
bay-head bar, 303 
bay-mouth bar, 302 
compound cuspate bar, 322 



Bars, cuspate bar, 318 
cuspate foreland bar, 324 
cuspate offshore bar, 383 
flying bar, 327 
looped bar, 309 
marine forces in development of 

bars, 328 
marsh bar, 325-327 
mid-bay bar, 303 
offshore bar, 259, 301, 350, 405 
submarine bar, 349 
V-bar, 322 

see also Shoreline, development 
of 
Bay bar, 300, 351 
see also Bars 
delta, 328 
see also Deltas 
Bay-head bar, 303 

see also Bars 
Bay-head beach, 285 
see also Beaches 
Bay-mouth bar, 302 

see also Bars 
Bay-side beach, 285 
see also Beaches 
Beach cusp, 224, 458-486 
see also Cusps, beach 
drifting, 94-103 

see also Current action 
plain, 297, 405 

profile of equilibrium, 217, 407 
see also Equilibrium 



567 



568 



INDEX — SUBJECTS 



Beach ridge, 297 

see also Shoreline, development of 
Beaches, 159-163, 215, 223, 259, 283- 
285 
barrier beach, 259 
bay-head beach, 285 
bay-side beach, 285 
storm beach, 223 

see also Shoreline development 
of; Terminology and classifica- 
tion of shores 
Beach, storm, 223 
Beaumont's, de, theory, 360 
Bench, 162, 203, 224, 258 

see also Shore profile, develop- 
ment of; Terminology and 
classification of shores 
Berge, Monadnock, 166 
Bottom drag, 16 
Boundary waves, 2, 44-45 
see also Waves, water 
Breaker, 16-20 
depth, 18-20 

see also Oscillation, waves of; 
Waves, water 
Bruckner's theory of 35-year cycle, 
411 

Canaveral, Cape, 405, 519-524 
Capillary waves, 7 

see also Oscillation, waves; 
Waves, water 
Carolinas, dunes of the, 519-524 
Chesil bank, the, 217 

see also Shore profile, develop- 
ment of 
Cinque ports, the, 424 
Classification of shores, 169-192 
genetic methods, 170-171 
numerical methods, 170-173 
compound shores, 190-192 
emergence shores, 186-187 
neutral shores, 187-190 

(see also Neutral shores) 
submergence shores, 173-186 
(see also Submergence, shores 
of; Terminology and classi- 
fication of shores) 



Cliffs, 160-161, 203, 224, 259, 349 

retrograding cliff, 295 
Coast, 160 
Coast-line, 159-160 
Coastal plane, 166 
Combined shore profile, 265-266 

see also Shore profile, develop- 
ment of 
Combined waves, 25-27, 36-38 

see also Oscillation, waves of; 
Waves, water 
Combing waves, 16 

see also Oscillation, waves of; 
Waves, water 
Complex cuspate foreland, 325 
see also Forelands 
spit, 290 

see also Spits 
tombolo, 431 

see also Tombolos 
Compound cuspate bar, 322 

see also Bars 
Compound recurved spit, 290, 416- 
419 
Dune ridge spit, 418 
low and narrow ridge spit, 416 
parallel ridge spit, 416 
single beach spit, 419 
see also Spits 
Compound shores, 190-192, 265-266, 
400-403 
see also Shore profile, develop- 
ment of; Shoreline, develop- 
ment of, Stages in develop- 
ment of shores; Terminology 
and classification of shores 
Compound spit, 405 

see also Spits 
Continental shelf, 163 

terrace, 163 
Contraposed shorelines, 401 

see also Shoreline, development 
of 
Convection current, 131 

see also Current action 
Coral reef, 188-189, 263 
see also Reefs 



INDEX — SUBJECTS 



569 



Current action, 1, 87-158, 407 

beach drifting, 94-103 

causes of currents, 87-88 

characteristics of currents, 1, 89 

complexities of current action, 141- 
143 

conflicting opinions re current 
action, 143-148 

convection currents, 131 

debris deposited by tidal currents, 
113-115 

debris moved by tidal currents, 
115-121 

deflection of currents, 141 

eddy currents, 139-141 

effects of longshore currents, 222 

hydraulic tidal currents, 121-122 

hydraulic wind currents, 124-125 

longshore currents, 407 

planetary currents, 128-130 

pressure currents, 130-131 

reaction currents, 138-139 

river currents, 136-138 

salinity currents, 131-136 
(see also Salinity currents) 

seasonal currents, 126-128 

Seiche currents, 122-123 

temporary currents, 125-126 

tidal currents, 2, 106-122 
(see also Tidal currents) 

types of currents, 87-90 

wave currents, 90-106 
(see also Wave currents) 

wind currents, 123-128 

(see also Wind currents) 

References, 149-158 

see also, under Index — Authors: 

Abbe, C; Agassiz, A.; Airy, 

G. B.; Andeison, J.; Andrews, 

E.; Anonymous; Austen, R. 

A. C; Bache, A. D.; Bailey, 

L. W.; Barnes, H. T.; Beaze- 

ley, A.; Belcher, E.; Bjerknes, 

V. and Sandstrom, J. W.; 

Branner, J. C; Bremontier, 

N. T.; Browne, W. R.; Bu- 

chan, A.; Buchanan, G. Y.; 

Buchanan, J. Y.; Bunt, Calig- 



ny, A. de; Carpenter, W. B. 
Cold, C; Coode, J.; Cornag 
lia, P.; Cornish, V.; Cronan- 
der, A. W.; Crosby, W. O. 
Dall, W. H.; Dana, J. D. 
Davis, C. H.; Dawson, J. W. 
Dawson, W. B.; Douglas, J 
N.; Ekman, F. L.; Ekman 
V. W.; Fischer, T.: Fleming 
S.; Gaillard, D. D.; Gardiner 
J. S.; Geikie, A.; Gibbs, J. 
Grabau, A. W.; Gulliver, F 
P.; Hallet, H. S.; Harring- 
ton, M. W.; Harris, R. A. 
Harrison, J. T.; Haupt, L. M. 
Helland-Hansen, B.; Nansen 
F.; Hunt, A. R.; Hunt, E. B. 
Kinahan, G. H.; Kinahan, H 
C; Kriiger, G.; Krummel, O. 
Le Conte, J.; Lindenkohl, A. 
Marten, H. J.; Matthews, E 
R.; Maury, M. F.; Mill, H 
R.; Mitchell, H.; Murray, J. 
Murray J. and Hjort, J. et al. 
Nares, Capt.; Oldham, J. 
Otto, T.; Owens, J. S. and 
Case, G. O.; Palmer, H. R. 
Parsons, H. de B.; Pechuel- 
Loesche; Perkins, F. W.; Pet- 
terson, O.; Philippson, A. 
Prestwich, J.; Reade, T. M. 
Reclus, E.; Redman, J. B. 
Rendel, J. M.; Rennie, G. 
Richardson; Robinson; Riihl 
A.; Russell, J. S.; Salisbury 
R. D.; Sandstrom, J. W 
Shaler, N. S.; Shield, W. 
Skertchley, S. B. J.; Sollas 
W. J.; Spratt; Stevenson, T. 
Stokes, G. G.; Taylor, F. B. 
Thoulet, J.; Townsend, C 
McD.; Vaughan, T. W. 
Wheeler, W.H.; Whewell, W. 
Willis, B.; Wilson, A. W. G. 
Wilson, J. 

Current ripples, 494-512 
see also Ripple marks 

Currents, see Current action 



570 



INDEX — SUBJECTS 



Cuspate bar, 318 
Cuspate bar, see also Bars 
compound, 322 
see also Bars 
delta, 409 

see also Deltas 
foreland, 322, 409 

see also Forelands 
foreland bar, 324 

see also Bars 
offshore bar, 383 
see also Bars 
Cusplet, 228, 479 

see also Cusps, beach 
Cusps, beach, 224, 458-486 
artificial beach cusp, 475 
characteristics of beach cusp, 463 
cusplet, 479 

early studies re beach cusp, 458 
relation of beach cusp to shore 

activity, 474 
theories re origin of beach cusp, 476 
see also Shore Forms, Minor 
Cycle, Bruckner's 35-year, 411 
Cycles of development, 228, 242-257 
emergence, 247 
fluvial, 242-245 
land-form, 247 
marine, 242-257 
shoreline, 247 
Cycloidal waves, 13 

see also Oscillation, waves of; 
Waves, water 

Darss, the, 404, 428, 519-524 

see also Shore forms, minor 
Debris, 113-125 

Deposition by tidal currents, 113-115 
movement by tidal currents, 115- 
121 
see also Talus 
Deflection, 141, 307 

current deflection, 141, 307 
stream deflection, 307 
Deltas, 187-190, 263, 395 , 
bay delta, 328 
cuspate delta, 409 
tidal delta, 374 



Deltas, wave-delta, 306 

see also Shore profile, develop- 
ment of; Shoreline, develop- 
ment of; Terminology and 
classification of shores 
Denmark, dunes of, 519-524 
Denudation, 166-169 
pluvio-fluvial, 166 
subaerial, 166-169 
Aeolian, 166-169 
fluvial, 166-169 
Deposition, 113-115, 162-163, 238 
backshore terrace, 163 
beach, 159-163 
continental shelf, 163 
continental terrace, 163 
effect, 238 

shoreface terrace, 163, 259 
tidal currents, 113-115 
veneer, 163 
Deposits, see Deposition 
Depth, of break wave, 18-20 

of wave action, 76-83 
Development of shore profile; see 
Shore profile, development of 
stages in; see Stages in develop- 
ment of shores 
Development of shoreline; see Shore- 
line, development of 
stages in ; see Stages of development 
of shores 
Domes, sand, 518-519 

see also Shore forms, minor 
Double tombolo, 315 

see also Tombolos 
Drew's map, of ridges, 422 
Drift, shore, 259, 352 
Drifting, beach, 94-103 
Drowned valley, 272 
see also Valleys 
Dune ridge, 404, 411, 418 

valley, 404 
Dunes, shore, 519-524 

Baltic Sea, dunes of the, 519-524 
Canaveral, dunes of Cape, 519-524 
Carolinas, dunes of the, 519-524 
Darss, dunes of the, 519-524 
Denmark, dunes of, 519-524 



INDEX — SUBJECTS 



571 



Dunes, Landes, dunes of the, 519-524 
Netherlands, dunes of the, 519-524 
Provincetown, dunes of, 519-524 
sand dunes, 519-524 
Sandy Hook, dunes of, 519-524 
Swinemunde, dunes of the, 519-524 
wind dunes, 519-524 

see also Shore forms, minor 

Dungeness, the, 404, 419 
see also Ridges, shore 

Dynamometer, wave, 62-63 

Earthquake and explosion waves, 2, 
38-41 
height, 40-41 (see also Height of 

waves) 
motion, 38-40 (see also Motion of 

waves) 
nature, 38-40 

origin, 38-40 (see also Origin of 
waves) 
see also Waves, water 
Eddy currents, 139-141 

see also Current action 
Elevation, progressive, 386 
Embankment, 285 

Emergence, shores of, 186-187, 258- 
262, 348-391, 408 
see also Shore profile, develop- 
ment of; Shoreline, develop- 
ment of; Stages in develop- 
ment of shoreline; Termi- 
nology and classification of 
shores 
Energy, wave, 56-57 

conditions affecting energy, 72-74 
kinetic energy, 56 
measurement of energy, 63-65 
potential energy, 56 
see also Waves, work of 
Equilibrium, beach profile of, 217, 
407 
profile of, 225 
zone of, 300 
Erosion forms, 160-162 
abrasion platform, 162 
bench, 162 
cliff, 160-161 



Erosion forms, see also Terminology 

and classification of shores 
Explosion waves, earthquake and, 2, 
38-41 
height, 40-41 (see also Height of 

waves) 
motion, 38-40 (see also Motion of 
I waves) 
nature, 38-40 

origin, 38-40 (see also Origin of 
waves) 
see also Waves, water 

Fault shores, 189-190, 264, 397 

see also Neutral shores 
Fetch, 22 
Fjord shorelines, 176-186 

see also Submergence, shores of 
Fluvial denudation, 166-169 
Fluvial peneplane, 166 
plain, 164-169 
planation, 249 
Flying bar, 327 

see also Bars 
Forelands, 322-325, 405 

complex cuspate foreland, 325 
cuspate foreland, 322, 409 
simple cuspate foreland, 325 
truncated cuspate foreland, 325 
see also Shoreline, development of 
Foreshore, 161 

Form, of waves, 12-21, 33-34 
waves of oscillation, 12-21 
breaker, 16-20 
cycloidal, 13 
intersecting, 20-21 
surf, 16 
swell, 15 
trochoidal, 13 
waves of translation, 33-34 

see also Oscillation, waves of; 
translation waves of 
Formulae, re waves, 15, 20, 21, 23, 27, 

28, 31, 32, 56 
Frequency of waves, 30 
Fulcrum, 295 
Fulls, 404, 411 
neap tide full, 411 



572 



INDEX — SUBJECTS 



Fulls, spring tide full, 411 

summer full, 411 

winter full, 411 

see also Ridges, shore 
Furrow, 404 

Genetic methods of classification of 

shores, 170-173 
Gilbert's theory, re bars, 360 
Glacial peneplane, 166 

plain, 164-169 

plane, 166 
Ground swell, 15 

Hanging valley, 343 
see also Valleys 
Headland, winged, 303 
Height of waves, 21-27, 34 

oscillation, 21-27; effect of fetch, 
22; effect of wind duration, 
22; formulae, 21, 23; records, 
24 
translation, 34 

see also Oscillation, waves of; 
Translation, waves of; Waves, 
water 
Hydraulic currents, 121-125 
tidal, 121-122 
wind, 124-125 

see also Current action 

Initial stage; see Stages in develop- 
ment of shores 
Inlets, 355 

migrating inlet, 374 
tidal inlet, 307, 367-368 

see also Shoreline, development 
of 
Inshore, 161 
Intersecting waves, 20-21 

see also Oscillation, waves of; 
Waves, water 
Island, formation of, 272 

Kinetic energy, 56 

see also Energy, wave; Waves, 
work of 

Lagoon, 261, 350, 379 

Lames de Fond, 11 

Landes, dunes of the, 519-524 



Length, of waves, 27-29, 35 
oscillation, 27-29 
records, 28-29 
waves, translation, 35 

see also Oscillation, waves of; 
Translation, waves of; Waves, 
water 
Level, of ridges, 439-453 
Lewin's map, of ridges, 426 
Longshore current, 222, 407 
Looped bar, 309 

see also Bars 
Lows and balls, 486-489 
parallel balls, 487-488 

see also Shore forms, minor 

Marks, 489-517 

backwash mark, 517 
lill mark, 512-513 
Ripple mark, 489-512 
swash mark, 513-517 

see also Shore forms, minor 
Marsh, 379 
Marsh bar, 325 

see also Bars 
Mature stage; see Stages in develop- 
ment of shores 
Measurement, of wave energy, 63-65 
Mid-bay bar, 303 
see also Bars 
Migrating inlet, 374 

see also Inlets 
Minor shore forms; see Shore forms, 

minor 
Misdroy spit, 431 
see also Spits 
Monadnock, 165-169 
Monadnock-Berge, 166 

see also Terminology and classi- 
fication of shores 
Motion, of waves, 8-12, 34-35 
waves of oscillation, 8-12 
waves of translation, 34-35 

see also Oscillation, waves of; 
Translation, waves of; Waves, 
water 

Nantasket beach, 412 

see also Ridges, shore 



INDEX — SUBJECTS 



573 



Neap tide full, 411 

see also Fulls 
Ness, 422 

Netherlands, dunes of the, 519-524 
Neutral shores, 187-190, 262-265, 
395-400 
alluvial plain, 188 
coral reef, 188-189 
delta, 187-190 
fault, 189-190 
out wash plain, 188 
volcano, 188 

see also Shore profile, develop- 
ment of; Shoreline, develop- 
ment of; Stages in develop- 
ment of shores; Terminology 
and classification of shores 
Nip, 259, 349 

Numerical methods of classification 
of shores, 170-171 

Offset, 307 
Offshore, 161 

Offshore bar, 259, 301, 350-405 
cuspate offshore bar, 383 

(see also Bars) 
development, 365 
not evidence of subsidence, 380 
retrogression, 380 
see also Bars 
Old stage; see Stages in development 

of shores 
Orbits of waves, 11-12 
Origin, of waves, 1, 7-8, 33 
capillary waves, 7 
earthquake and explosion waves, 

38-40 
waves of oscillation, 7-8 
waves of translation, 8 

see also Oscillation, waves of; 
Translation, waves of; Waves, 
water 
Oscillation, waves of, 1, 7-33 

depth of break, 18-20 (see also 

Breaker) 
effect of wind upon fetch, 22 
form (see also Form of waves) 
formulae, 21-32 



Oscillation, frequency, 30 

height, 21-27 (see also Height of 

waves) 
length, 27-29 (see also Length of 

waves) 
motion, 8-12 (see also Motion of 

waves) 
orbits, 11-12 
origin, 7-8 (see also Origin of 

waves) 
period, 30 
surf, 16 

swell (ground-swell), 15 
velocity, 29-33 (see also Velocity of 
waves); breaker, 16-20; com- 
bined wave, 25-27; combing 
wave, 16; cycloidal wave, 13; 
intersecting wave, 20; tro- 
choidal wave, 13 
see also Waves, water 
Oscillation ripples, 494-512 

see also Ripple marks 
Out wash plain, 188 
Overlap, 307-308 

Peneplain, 159, 164-169 

aeolian, 164-169 

fluvial, 164-169 

glacial, 164-169 

marine, 164-169 
Peninsulas, formation of, 272 
Period, of waves, 30 
Plain, 159, 164-169 

aeolian, 164-169 

alluvial outwash, 263 

beach, 297, 405 

fluvial, 164-169 

glacial, 164-169 

marine, 164-169 
see also Plane 
Planation, 199, 249-253 

fluvial, 249-253 

marine, 249-253 
Plane, 159, 164-169 

aeolian, 164-169 

coastal, 166 

fluvial, 164-169 

glacial, 164-169 



574 



INDEX — SUBJECTS 



Plane, marine, 164-169 . 

see also Plaii. 
Planetary currents, 128-130 

see also Current action 
Platform, abrasion, 162, 225 
Pluvio-fluvial denudation, 166 
Potential energy, 56 

see also Energy, wave; Waves, 
work of 
Pressure currents, 130-131 

see also Current action 
Profile of equilibrium, 225 
Prograding shore, 223 
Progression and retrogression of 

ridges, 409 
Progression of shore, 223 
Progressive elevation of shore, 386 

subsidence of shore, 383 
Provincetown, dunes of, 519-524 

Reaction currents, 138-139 
see also Current action 
Recurved spit, 290, 405 
see also Spits 
compound, 290, 416 
Reefs, 188, 259-308 
coral reef, 188-189 
sand reef, 259 
stone reef, 308 

see also Shore profile, develop- 
ment of 
References, current action, 149-159 
shore ridges, 454-457 
shore forms, minor, 525-532 
shore profile, development of, 268- 

271 
shoreline, development of: 
emergence, 392-394 
neutral and compound, 403 
submergence, 345-347 
terminology and classification of 

shores, 192-198 
waves, water, 46-54 
waves, work of, 83-86 

see also References, under heads 
above, for authorities 
Refraction, wave, 74-76 
see also Waves, work of 



Retrograding cliff, 295 
see also Cliffs 

shore, 223 
Retrogression and progression of 

ridges, 409 
Retrogression of offshore bars, 380 

of shores, 223 
Ria shorelines, 173-176 

see also Submergence, Shores of 
Ridge, single beach, 419 
Ridges, shore, 404-457 

Appach's map of bridges, 426 

beach plain, 405 

beach ridge, 297 

beach profile of equilibrium, 407 

Bruckner's 35-year cycle, 411 

Cape Canaveral, 405 

Cinque Ports, 424 

complex tombolo, 431 

compound recurved spit, 416 

compound spit, 405 

cuspate delta, 409 

cuspate foreland, 409 

Darss, 404, 428 

Drew's map of ridges, 422 

Dune ridge, 404, 411, 418 

dune valley, 404 

Dungeness, 404, 419 

foreland, 405 

fulls, 404 

(see also Fulls) 

furrow, 404 

level of ridges, 439-453 

Lewin's map of ridges, 426 

longshore current, 407 

low and narrow ridges, 416 

misdroy spit, 431 

Nantasket beach, 412 

Ness, 422 

offshore bar, 405 

origin of ridges, 404-414 

parallel ridges, 416 

progression and retrogression oi 
shores, 409 

rate of formation of ridges, 414-439 

Rinnen, 422 

recurved spit, 405 

Rockaway beach, 416 



INDEX — SUBJECTS 



575 



Ridges, shoreline of emergence, 408 
shoreline of submergence, 409 
single beach ridge, 419 
slash, 404 
swale, 404 

Swinemunde spit, 431 
tombolo, 411 
Wallen, 422 
waves of translation, 
wave-terrace, 405 
References, 454-457 
see also under Index — Authors : 
Appach, F. H.; Beaurain, G.; 
Braun, G.; Bruckner; Bur- 
rows, M.; Cornish, V.; Cub- 
itt, W.; Davis, W. M.; Drew 
F.; Ganong, W. F.; Gilbert 
G. K.; Goldthwait, J. W. 
Gulliver, F. P.; Howlett, B. S. 
Johnson, D. W. and Reed, W 
G.; Keilhack, K.; Kriiger 
G.; Lewin, T.; Otto, T. 
Redman, J. B.; Robertson 
W. A. S.; Sokolow, N. A. 
Solger, F., et at.) Wheeler, 
W. H. 
Rill marks, 512-513 

see also Shore forms, minor 
Rills, 512-513 

see also Mark 
Rinnen, the, 422 
Ripple marks, 489-512 

asymmetrical ripples, 494-512 
current ripples, 494-512 
oscillation ripples, 494-512 
symmetrical ripples, 494-512 
theories re causes of ripple mark, 

489 
tidal ripples, 498-500 

see also Shore forms, minor 
Ripples, 489-512 

see also Marks 
River currents, 136-138 

see also Current action 
Rockaway beach, 416 

Salinity currents, 131-136 

at mouth of Baltic Sea, 133-134 



Salinity currents, at St. of Bab-el- 
Mandeb, 136 
at St. of Gibraltar, 134-136 
see also Current action 
Sand domes, 518-519 

see also Shore forms, minor 
Sand dune, 519-524 

see also Dunes, shore 
Sand reef, 259 

see also Reefs 
Sand spit, 301 

see also Spits 
Sandy Hook, dunes of, 519-524 
Seasonal currents, 126-128 
see also Current action 
Seiche currents, 122-123 

see also Current action 
Seiche waves, 42-43 

see also Waves, water 
Serpentine spit, 291 

see also Spits 
Shelf, continental, 163 
Shingle, 163 
Shore, 160 

Shore, prograding, 223 
Shore, retrograding, 223 
Shore drift, 259, 352 
Shore dunes, 519-524 

see also Dunes, shore 
Shore forms, minor, 458-532 
backwash marks, 517 
beach cusps, 458-486 

(see also Cusps, beach) 
domes, 518-519 
dunes, 519-524 

(see also, Dunes, shore) 
lows and balls, 486-489 

(see also Lows and balls) 
rill marks, 512-513 
ripple marks, 489-512 

(see also Ripple marks) 
swash marks, 513-517 
tidal ripples, 498-500 
References, 525-532 

see also, under Index — Authors : 
Agassiz, A ; Andrews, E.; 
Ayrton, H.; Barrell, J.; Beau- 
rain, G.; Beche, H. T. de la; 



576 



INDEX — SUBJECTS 



Berendt, G.; Branner, J. C. 
Braun, G.; Bremontier, N. T. 
Brown, A. P.; Bucher, W. H. 
Candolle, C. de; Cobb, C. 
Cornish, V.; Cushing, H. P. 
Damant, Lt.; Darwin, G. H. 
Desor, E.; Dodge, R. E. 
Epry, C; Fairchild, H. L. 
Foerste, A. F.; Forel, F. A. 
Gaudry, A.; Gilbert, G. K. 
Gilmore, J.; Grabau, A. W. 
Hagen, G.; Hitchcock; Hunt 
A. R.; Hyde, J. E.; Jagger 
T. A. Jr.; Jefferson, M. S. W. 
Johnson, D. W.; Kemp, J. F. 
Kindle, E. M.; Kindle, E. M 
and Taylor, F. B.; Lane, A 
C; Latrobe, B. H.; Lehmann 
F.W.P.; Locke, J.; Lyell, C. 
Merrill, F. J. H.; Miller, W 
J.; Moore, J. and Hole, A. D. 
Nathorst, A. G.; Otto, T. 
Owens, J. S.; Palmer, H. R. 
Pierce, R. C; Prosser, C. S. 
Reade, T. I.; Reynolds, O. 
Russell, I. C; Saporta, G. de 
Scrope, G. P.; Shaler, N. S. 
Shannon, W. P.; Siau; Soko- 
low, N. A.; Solger, F., et al.; 
Sorby, H. C; Udden, J. A.; 
Van Hise, C. R.; Wheeler, 
W. H.; Whittlesey, C; Wil- 
liamson, W. C; Wilson, A. 
W. G.; Wooster, L. C. 
Shore profile, development of, 199- 
271 
compound shores, 265-266 

stages in development, 265-266 
(see also Stages in develop- 
ment of shores) 

see also Compound shores 
emergence shores, 258-262 

barrier beach, 259 

lagoon, 261 

marine bench, 258 

marine cliff, 259 

nip, 259 

offshore bar, 259 



Shore profile, offshore barrier, 259 
sand reef, 259 
shore drift, 259 
shoreface terrace, 259 
stages in development, 258-262 

(see also Stages in develop- 
ment of shores) 
see also Emergence, shores of 
neutral shores, 262-265 
alluvial outwash plain, 263 
coral reef, 263 
delta, 263 
fault, 264 
shoreface, 263 
stages in development, 262-265 

(see also Stages in develop- 
ment of shores) 
see also Neutral shores 
submergence shores, 199-258 
abrasion platform, 225 
beach, 215 
beach cusp, 224 
beach profile of equilibrium, 

217 
bench, 203, 224 
cliff, 203, 224 
cycles of development, 242-257 

(see also Cycles of develop- 
ment) 
effect of deposition, 238 

(see also Deposition) 
effects of longshore currents, 222 

(see also Current action) 
planation, 249 

(see also Planation) 
profile of equilibrium, 225 
prograding shore, 223 
retrograding shore, 223 
stages in development, 203-258 

(see also Stages in develop- 
ment of shores) 
storm beach, 223 
storm terrace, 223 
talus, 203 
terrace, 224 

theory of marine abrasion, 234 
theory of marine cycle, 228 
wave base, 225 



INDEX — SUBJECTS 



577 



Shore profile, see also Shoreline, de- 
velopment of; Terminology 
and classification of shores 
see also Submergence, shores of 
References, 268-271 
see also under Index — Authors 
Andrews, E.; Austen, R. A 
C; Beaumont, E. de; Coode 
J.; Cushing, S. W.; Daly, R 
A.; Davis, W. M.; Fenneman 
N. M.; Fischer, T.; Geikie, A. 
Gilbert, G. K.; Green, A. H. 
Gulliver, F. P.; Haage, R. 
Hahn, F. G.; Helland-Hansen 
B.; Hunt, A. R.; Johnson, D 
W.; Johnson, D. W. and Reed 
W. G.; Jukes-Browne, A. J. 
Kayser, E.; Kinahan, G. H. 
Lapparent, A. de; Lawson 
A. C.; Marindin, H. L.; Mar 
tonne, E. de; Mitchell, H. 
Murray, J.; Nansen, F.; Nuss- 
baum, F.; Otto, T.; Pendle- 
ton, A. G.; Ramsay, A. C. 
Rankine, W. J. M.; Reed, W 
G.; Reusch, H.; Richter, E. 
Richthofen, F. von; Scott, W 
B.; Shaler, N. S.; Shield, W. 
Stevenson, R.; Vogt, J. H. L. 
Wharton, W. J. L,; Wheeler 
W. H.; Williams, H. S. 
Wright, W. B. 
Shore ridges, 404-457 
see Ridges, shore 
Shoreface, 263 

terrace, 163, 259 
Shoreline, 159 

high tide shoreline, 161 
low tide shoreline, 161 
Shoreline, development of, 272-403 
compound shorelines, 400-401 
(see also, below, Neutral and com- 
pound shorelines) 
contraposed shorelines, 401-403 
(see also, below, Neutral and com- 
pound shorelines) 
emergence shorelines, 348-394 



Shoreline, emergence, bars,- 350-390 

(see also Bars) 
barrier, 352 
barrier-bar, 352 
bay bar, 351 
Beaumont's, de, theory re shores, 

360 
cliff, 349 

cuspate offshore bar, 383 
Gilbert's theory re shores, 360 
inlets, 355 

(see also Inlets) 
key, 351 . 
lagoon, 350, 379 
marsh, 379 
migrating inlet, 374 
nip, 349 

offshore bar, 350-390 
progressive elevation, 386 
progressive subsidence, 383 
shore drift, 352 

stages in development, initial 
stage, 348-350 

young stage, 350-389 

mature stage, 389-390 

old stage, 390-391 

(see also Stages in develop- 
ment of shores) 
submarine bar, 349 
tidal delta, 374 
tidal inlet, 367 

see also Emergence, shores of 
References, 392-394 
see also, under Index — Authors 

Abbe, C. Jr.; Agassiz, L. 

Beaumont, E. de; Bryson, J. 

Davis, C. A.; Davis, W. M. 

Ganong, W. F.; Gilbert, G. 

K.; Goldthwait, J. W.; Gul- 
liver, F. P.; McGee, W. J.; 

Merrill, B. M.; Merrill, F. J. 

H.; Mudge, B. F.; Russell, I. 

C.; Schott, A.; Shaler, N. S.; 

Weidemuller, C. R.; White, D. 
Neutral shorelines, 395-400 

(see also, below, Neutral and 

compound shorelines) 
delta, 395 



578 



INDEX — SUBJECTS 



Shoreline, neutral, fault, 397 

Neutral and compound shorelines, 

395-403 
compound shorelines, 400-401 
contraposed shorelines, 401-403 
neutral shorelines, 395-400 
stages in development, 395-403 

(see also Stages in develop- 
ment of shores) 

see also Neutral and com- 
pound shores 
References, 403 
see also, under Index — Authors : 

Barrell, J.; Clapp, C. H.; 

Cotton, C. A.; Credner, G. R. 
submergence shorelines, 272-347 
bars, 300-340 (see also Bars) 
bay bar, 300 
bay delta, 328 
bay-head bar, 303 
bay-head beach, 285 
bay-mouth bar, 302 
bay-side beach, 285 
beaches, 283-300 

(see also Beaches) 
beach plain, 297 
beach ridge, 297 
complex cuspate foreland, 325 
complex spit, 290 
compound cuspate bar, 322 
compound recurved spit, 290 
cuspate bar, 318 
cuspate foreland, 322 
cuspate foreland bar, 324 
deltas, 306, 328 

(see also Deltas) 
double tombolo, 315 
drowned valley, 272 
embankment, 285 
flying bar, 327 
forelands, 322-325 

(see also Forelands) 
fulcrum, 295 
hanging valley, 343 
island, 272 

irregular sea-bottom and shore- 
line, 272 
looped bar, 309 



Shoreline, submergence, marsh bar, 
325 
mid-bay bar, 303 
offset, 307 
offshore bar, 301 
overlap, 307 
peninsula, 272 
recurved spit, 290 
retrograding cliff, 295 
sand spit, 301 
serpentine spit, 291 
simple cuspate foreland, 325 
spits, 287-302 

(see also Spits) 
stages in development, initial 
stage, 272-275 
young stage, 275-339 
mature stage, 339-344 

old stage, 344 

(see also Stages in develop- 
ment of shores) 
stone reef, 308 
stream deflection, 307 
tombolos, 310-320 

(see also Tombolos) 
tidal inlet, 307 

truncated cuspate foreland, 325 
Valleuse, 343 
valleys, 272, 343 

(see also Valleys) 
V-bar, 322 
wave-delta, 306 
winged headland, 303 
Y-tombolo, 315 
zone of equilibrium, 311 

see also Submergence, shores of 
References, 345-347 
see also, under I ndex — Authors : 

Abbe, C; Beaufort, F.; Beche, 

H. T. de la; Branner, J. 

C; Cold, O.J Comstock, F. 

N.j Dana, J. D.; Davis, W. 

M.; Duane, J. C, et al.; 

Ewart, F. C; Fleming, S.; 

Gilbert, G. K.; Gulliver, F. 

P.; Hentzschel, O.; Hind, H. 

Y.; Hobbs, W. H.; Johnson, 

D. W. and Reed, W. G.; 



INDEX — SUBJECTS 



579 



Livingston, A. A.; Marinelli, 
O.; Petrocchi; Philippson, S.; 
Pianigiani, O.; Ranee, de; 
Ricchieri, G.; Richthofen, F. 
von; Shaler, N. S.; Tarr, R. 
S.j Wheeler, W. H.; Wilson, 
A. W. G.; Woodman, J. E. 
Shorelines, delta, 395 

fault, 397 
Shores, classification of, see Classifi- 
cation of shores; Terminology 
and classification of shores 

compound, 190-192, 265-266, 400- 
403 
see also Shore profile, develop- 
ment of; Shoreline, develop- 
ment of; Stages in develop- 
ment of shores; Terminology 
and classification of shores 

emergence, 186-187, 258-262, 348- 
391 
see also Shore profile, develop- 
ment of; Shoreline, develop- 
ment of; Stages in develop- 
ment of shores; Terminology 
and classification of shores 

neutral, 187-190, 262-265, 395-400 
see also Shore profile, develop- 
ment of; Shoreline, develop- 
ment of; Stages in develop- 
ment of shores; Terminology 
and classification of shores 

submergence, 173-186, 199-258, 
272-344 
see also Shore profile, develop- 
ment of; Shoreline, develop- 
ment of; Stages in de- 
velopment of shores; Ter- 
minology and classification of 
shores 

terminology and classification of; 
see Terminology and classifi- 
cation of shores 

terminology of; see Terminology 
of shores; Terminology and 
classification of shores 
Simple cuspate foreland, 325 
see also Forelands 



Single beach ridge, 419 

see also Ridges, shore 
Slash, 404 

Spits, 287-300, 404-439 
complex spit, 290 
compound spit, 405 
compound recurved spit, 290, 416 
(see also Compound recurved 
spit) 
misdroy spit, 431 
recurved spit, 290, 405 
sand spit, 301 
serpentine spit, 291 
Swinemtinde spit, 431 

see also Shoreline, development 
of; Ridges, shore 
Spring tide full, 411 

see also Fulls 
Stages in development of shores, 190, 
201-266, 272-344, 348-391, 
395-403 
initial stage; compound profile, 
265-266 
compound shoreline, 400-403 
emergence profile, 258-259 
emergence shoreline, 348-350 
neutral profile, 262-265 
neutral shoreline, 395-400 
submergence profile, 201-203 
submergence shoreline, 272-275 
young stage; compound profile, 
265-266 
compound shoreline, 400-403 
emergence profile, 259-262 
emergence shoreline, 350-389 
neutral profile, 262-265 
neutral shoreline, 395-400 
submergence profile, 203-210 
submergence shoreline, 275-339 
mature stage; compound profile, 
265-266 
compound shoreline, 400-403 
emergence profile, 262 
emergence shoreline, 389-390 
neutral profile, 262-265 
neutral shoreline, 395-400 
submergence profile, 210-224 
submergence shoreline, 339-344 



580 



INDEX — SUBJECTS 



Stages in development of shores, old 
stage; compound profile, 265- 
266 
compound shoreline, 400-403 
emergence profile, 262 
emergence shoreline, 390-391 
neutral profile, 262-265 
neutral shoreline, 395-400 
submergence profile, 224-258 
submergence shoreline, 344 
see also Shore profile, develop- 
ment of; Shoreline, develop- 
ment of; Terminology and 
classification of shores 
Standing waves, 42-43 
seiches, 42-43 

see also Seiches; Waves, water 
Storm beach, 223 

see also Beaches 
Storm terrace, 223 

see also Terraces 
Storm waves, damage done by, 65-72 

see also Waves, work of 
Strand, 159 
Strandline, 159 
Stream deflection, 307 
Subaerial denudation, 166 
aeolian, 166 
fluvial, 166 
Submarine bar, 322, 349 

see also Bars 
Submergence, shores of, 173-186, 
199-258, 272-344 
Ria shorelines, 173-176 
Fjord shorelines, 176-186 

see also Shore profile, develop- 
ment of; Shoreline, develop- 
ment of; Stages in develop- 
ment of shoreline; Termi- 
nology and classification of 
shores 
Subsidence, progressive, 383 
Summer full, 411 
see also Fulls 
Surf, 16 
Swale, 404 
Swash, 513-517 



Swash marks, 513-517 

see also Marks, minor 
Swell, 15 

Swinemunde, dunes of the, 519-524 
spit, 431 
tombolo, 431 
Symmetrical ripples, 494-512 
see also Ripple marks 

Talus, 203 

see also Debris 
Temporary currents, 125-126 

see also Current action 
Terminology and classification of 
shores, 159-198 
abrasion platform, 162, 225 
backshore terrace, 163 
beach, 159-163 
bench, 162 
classification of shores, 169-192 

(see also Classification of shores) 
cliff, 160-161 
coast, 160 

compound shores, 190-192 
continental shelf, 163 

terrace, 163 
coral reef, 188-189 
delta, 187-190 
denudation, 166-169 

(see also Denudation) 
deposition, 113-115, 162-163, 238 
1 (see also Deposition) 
emergence shores, 186-187 
erosion forms, 160-162 

(see also Erosion forms) 
fault shores, 189-190 
fjord shorelines, 176-186 
genetic methods of classification of 
shores, 170-173 

(see also Classification of shores) 
inshore, 161 
Monadnock, 165-169 
neutral shores, 187-190 

(see also Neutral shores) 
numerical methods of classification 
of shores, 170-171 

(see also Classification of shores) 
offshore, 161 



INDEX — SUBJECTS 



581 



Terminology and classification of 
shores, peneplain, peneplane, 
plain, plane, 159, 164-169 
(see also Peneplain, Peneplane, 
Plain, Plane) 

Ria shorelines, 173-176 

shingle, 163 

shore, 160 

shoreface terrace, 163, 259 

shoreline, 159 

stages in development. 190 

submergence shores, 173-186 
(see also Submergence, shores of) 

terminology of shores, 159-169 
(see also Terminology of shores) 

veneer, 163 

volcano shores, 188 

water line, 159 

zones, 159-161 
(see also Zones) 
References, 192-198 
see also, under Index — Authors 
Agassiz, A.; Andrews, E. C. 
Barrell, J.; Berghaus, H. 
Brogger, W. C; Brown, R. 
Cold, C; Cotton, C. A. 
Daly, R. A.; Dana, J. D. 
Darwin, G. H.; Davis, W. M. 
Davis, W. M. and Wood, J 
W.; Dinse, P.; Dutton, C. E. 
Esmark, J.; Fairchild, H. L. 
Fischer, T.; Gallois, L.; Gan- 
nett; Gilbert, G. K.; Green, 
A. H.; Gregory, H. E., 
Keller, A. G. and Bishop, A. 
L.; Gregory, J. W.; Gross- 
man, K. and Lomas, J.; Gul- 
liver, F. P.; Gurlt, F. A 
Giittner, P.; Haage, R 
Haast, J. von; Hahn, F. G 
Helland, A.; Hentzschel, O 
Hirt,0.; Hobbs,W.H.; Hub- 
bard, G. D.; Hull, E.; John- 
son, D. W.; Jukes-Browne, 
A. J.; Kloden; Kornerup, A.; 
Laparent, A. de; Lawson, A. 
C; Le Conte, J.; Marshall, 
P.; Martonne, E. de; Mar- 



vine, A. R.; Meinhold, F 
Murray, J.; Murray, J. and 
Hjort, J. et at.; Nagel, C. H. 
Nordenskjold, O.; Passarge 
S.; Penck, A.; Peschel, O. 
Playfair, J.; PoweU, J. W. 
Ratzel, Fr.; Remmers, O. 
Reusch, H.; Reuschle; Rich- 
thofen, F. von; Riessen, P. 
Ritter, C; Schroter, W. 
Schwind, F.; Shaler, N. S. 
Steffen, H.; Suess, E.; Tarr 
R. S. ; Tayler, J. W. ; Upham 
W.; Vaughan, T. W.; Vogt, J 
H. L.; Weidemiiller, C. R. 
Werth, E. ; Weule, K. ; Wheeler, 
W. H. 
Terminology of shores, 159-169 
denudation, 166-169 

(see also Denudation) 
deposition, 159-164 

(see also Deposition) 
erosion forms, 160-162 

(see also Erosion forms) 
peneplanes, 164-169 

(see also Peneplanes) 
plains, 164-169 
planes, 164-169 

(see also Planes) 
zones, 159-161 

(see also Zones; Terminology 
and classification of shores) 
Terraces, 163, 223-224, 405 
backshore terrace, 163 
continental terrace, 163 
shoreface terrace, 163, 259 
storm terrace, 223 
wave-, 405 

see also Ridges, shore; Shore 
profile, development of; Ter- 
minology and classification of 
shores 
Tidal currents, 2, 106-122 
deposition of debris, 113-115 
hydraulic currents, 121-122 
movement of debris, 115-121 
see also Current action 



582 



INDEX — SUBJECTS 



Tidal delta, 374 

see also Deltas 
Tidal hydraulic current, 121-122 

see also Hydraulic currents 
Tidal inlet, 307, 367 

see also Inlets 
Tidal ripples, 498-500 

see also Ripple marks 
Tidal waves, 2, 41-42 
compound tidal wave, 41 
tidal wavelet, 41-42 
see also Waves, water 
Tide; see Tidal currents; Tidal 

waves 
Tombolos, 310, 315, 411, 431 
complex tombolo, 431 
double tombolo, 315 
the Swinemunde, 431 
triple tombolo, 315 
Y-tombolo, 315 

see also Ridges, shore; Shoreline, 
development of 
Translation, waves of, 1, 33-38, 408 
complexity, 36-38 
form, 33-34 

(see also Form of waves) 
height, 34 

(see also Height of waves) 
length, 35 

(see also Length of waves) 
motion, 34-35 

(see also Motion of waves) 
origin, 33 

(see also Origin of waves) 
velocity, 35-36 

(see also Velocity of waves; 
Waves, water) 
Triple tombolo, 315 

see also Tombolos 
Trochoidal waves, 13 

see also Oscillation, waves of; 
Waves, water 
Truncated cuspate foreland, 325 
. see also Forelands 

Valleuse, 343 

(see also Valleys) 



Valley, drowned, 272 
(see also Valleys) 
dune, 404 

(see also Valleys) 
hanging, 343 

(see also Valleys) 
Valleys, 272, 343, 404 
drowned valley, 272 
hanging valley, 343 
valleuse, 343 

see also Ridges, shore; Shoreline, 
development of 
V-bar, 322 

see also Bars 
Velocity of waves, 2, 29-33, 35-36 
waves of oscillation, 29-33 

(see also Oscillation, waves of) 
waves of translation, 35-36 

(see also Translation, waves of) 
Veneer, 163 
Volcanic shoreline, 188, 263 

Wallen, the, 422 
Water line, 159 
Wave action, depth of, 76-83 
Wave attack, nature of, 57-62 
Wave currents, 90-106 
beach drifting, 94-103 
hydraulic currents, 103-105 
work of currents, 105-106 
see also Current Action 
Wave delta, 306 

see also Deltas 
Wave energy, 55-74 

conditions affecting energy, 72- 
74 
measurement of energy, 63-65 
Wave erosion, 161-162 
abrasion platform, 162 
bench, 162 
cliff, 161 
Wave dynamometer, 62-63 
Wave-terrace, 405 

see also Terraces 
Waves, capillary, 7 

combined, 25-27, 36-38 
Waves of oscillation; see Oscillation, 
waves of 



INDEX — SUBJECTS 



583 



Waves of Translation; see Transla- 
tion, waves of 
Waves, orbits of, 11-12 

storm, damage done by, 65-72 
water, 1-54 

bottom drag, 16 

boundary waves, 2, 44-45 

breaker, 16-20 

capillary waves, 7 

characteristics of waves, 1 

combined waves, 25-27 

combing waves, 16 

cycloidal waves, 13 

depth at which waves break, 1, 

16-20 
earthquake waves, 2, 38-40 , 

(see also Earthquake and Ex- 
plosion waves) 
explosion waves, 2, 38-41 

(see also Earthquake and Ex- 
plosion waves) 
form of waves, 12-21, 33-34 

(see also Form of waves) 
. ground swell, 15 
height of waves, 21-27, 34 

(see also Height of waves) 
intersecting waves, 20-21 
length of waves, 27-29, 35 

(see also Length of waves) 
literature re waves, 1-7 
motion of waves, 8-12, 34-35 

(see also Motion of waves) 
nature of waves, 1 
origin of waves, 1, 7-8, 33 

(see also Origin of waves) 
oscillation waves, 1, 7-33 

(see also Oscillation, waves of) 
scope of subject, 2-4 
seiches, 42-43 
standing waves, 42-43 
surf, 16 
swell, 15 
tidal waves, 2, 41-42 

(see also Tidal waves) 
translation waves, 1, 33-38 

(see also Translation, waves 
of) 
trochoidal waves, 13 



Waves, water, types of waves, 7 

velocity of waves, 2, 29-33, 35-36 

(see also Velocity of waves) 
work performed by waves, 1 
(see also Waves, work of) 
References, 46-54 

see also under Index — 
Authors: Abercromby, R.; 
Airy, G. B.; Antoine, C; 
Bache, A. D.; Bazin, EL; 
Bertin, E.; Bois, C. des; 
Boussinesq, J.; Bremontier, 
N. T.; Caligny, A. de; 
Cialdi, A.; Cornaglia, P.; 
Cornish, V.; Darcy; Dar- 
win, G. EL; Darwin, L.; 
Dawson, W. B.; Ekman, V. 
W.; Emy, A. R.; Fenne- 
man, N. M.; Fleming, J. A.; 
Gaillard, D. D.; Gerstner, 
F.; Hagen, G.; Harris, R. 
A.; Haupt, L. M.; Helland- 
Hansen, B. and Nansen, F.; 
Hobbs, W.H.; Hunt, A. R.; 
Kelvin, Lord; Krummel, O.; 
Lagrange; Lyman, C. S.; 
Marsh, G. P.; M oiler; Mot- 
tez, A.; Newton; Paris, A.; 
Rankine, W. J. M.; Red- 
field; Reid, H. F.; Ross; 
Russell, J. S.; Saint- Venant, 
B. de; Sandstrom, J. W.; 
Schott, G.; Scoresby, W.; 
Stevenson, T.; Stokes, G. 
G.; Tanner, Z. L.; Taylor, 
F. B.; Thompson, W.', 
Thoulet, J.; Vinci, L. da; 
Weber, E. H. and W.; 
Wheeler, W. H.; White, 
W. H. 
work of, 55-86 

conditions affecting energy, 72-74 
damage by storm waves, 65-72 
depth of wave action, 76-83 * 
dynamometer, 62-63 
energy generated by waves, 55- 
57 
(see also Energy, wave) 









584 



INDEX — SUBJECTS 



63 fj- 
«7 



Waves, work of, kinetic energy, 56 
measurement of energy, 63-65 
nature of wave-attack, 57-62 
potential energy, 56 
refraction of waves, 74-76 

see also Waves, water 
References, 83-86 
see also, under Index — ■ 
Authors: Agassiz, A.; Airy, 
G. B.; Calver, E. K.; Ci- 
aldi, A.; Coode, J.; Cor- 
nish, V.; Davis, W. M.; 
Delesse, M.; Douglas, J. 
N.; Ekman, V. W.; Flem- 
ing, J. A.; Fol, H.; Forbes, 
E.; Gaillard, D. D.; Gei- 
kie, A.; Gilbert, G. K.; 
Hagen, G.; Harrison, J. T.; 
Henwood, W. J.; Hunt, A. 
R.; Kinahan, G. H.; Lap- 
parent, A. de; I /ell, C.; 
Matthews, E. R.; leunier, 
S.; Murray, J.; Na isen, F.; 
Playfair, J.; Roy.xl Com- 
mission on Coast Erosion; 
Shaler, N. S.; Shield, W.; 
Siau; Sorby, H. C; Steven- 
son, R.; Stevenson, T.; 
Thoulet, J.; Weber, E. H. 
and W.; Wheeler, W. H. 



Wind currents, 123-128 
hydraulic current, 124-125 
seasonal current, 126-128 
temporary, 125-126 
see also Current action 
Wind dunes; see Dunes, shore 
Wind hydraulic current, 124-125 

see also Hydraulic currents 
Winged headland, 303 
Winter full, 411 

see also Fulls** 
Work, of currents (see Current 
action) 
of waves (see Waves, work of) 

Young stage; see Stages in develop- 
ment of shores 
Y-tombolo, 315 

see also Tombolos 

Zone of equilibrium, 300 
Zones, 159-161 
coast, 159-160 
offshore, 161 
shore, 159-160 
backshore, 161 
foreshore, 161 
shoreface, 161 

see also Terminology and classi- 
fication of shores 



3477 
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